Windows XP Service Pack 3 is now available for download from Windows Update.
See the Technet article on installing Windows SP3. Note that they recommend having WinXP SP2 installed before installing SP3.

Having trouble with your .NET framework? I had a difficult time getting Windows Update to install Hotfix KB928366 on my computer. No matter what I did, I couldn’t uninstall or fix the .NET Framework. After a lot of Googling and trying different suggestions, here is what worked for me.
How to re-install the .NET Framework 1.1

Remove [...]

Installing Windows 98

Run Windows 98 from a CD
Driver Packs for Windows 98

Unattended Windows Installations

Create an Unattended Windows XP CD
Create a Multi-Boot DVD with every operating system and support tool you ever need
Integrate Microsoft Update into your install CD

Unattended Application Installations

The Great Unattended Project is an executable that silently downloads and installs commonly use freeware applications
Hardware [...]

During WinXP installation, if you try to access a network share at T-12 then you get a “Workstation is not running” error. Starting the workstation service manually with net start workstation reports the service is already running.

The the issue is that microsoft left out some info in the system hive so you need to edit [...]

Slashdot had a topic about the first 10 applications you install on a fresh PC.
Heres my suggestions.
For the paranoid, I’d recommend installing AVG antivirus and ZoneAlarm firewalls from CD, so that you are protected before you even connect to the internet.

Windows XP and Win2000 SP2 come with a font editor called eudcedit.exe, usually in your Windows\System32 folder. Although your new font may look blocky or pixellated, Windows estimates a better vector representation that can be seen by selecting Show Outline on the View menu.
Use charmap.exe to use your new characters.

Delete old files from all your Windows temporary folders in one fell swoop with Erasetemp from http://www.webattack.com/get/erasetemp.html
More free deleters at http://www.snapfiles.com/Freeware/system/fwdiskclean.html

CutePDF Printer is a free PDF generator from http://www.acrosoftware.com/
PDF995 from http://www.pdf995.com/ also lets you create PDF files for free. It creates files slightly smaller and easier to read than CutePDF, but you have to install Free Converter too, and it popups ads in your browser when you use it.

Using Outlook 2003 you can view the header and source together, if you edit a registry key. This works on mail obtained from Internet mail transports, not Exchange server mailboxes. However, if you access the mailbox using an Internet transport, you’ll see the full source.

Open the registry editor and navigate to:

HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Options\Mail
right click on the right [...]

If you want to “tray” Outlook you need to create this registry key and set the value of MinToTray to 1.
[HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Preferences]
“MinToTray”=dword:00000001

Force Outlook to display mails in plain text to reduce the risk of html viruses carrying dangerous vulnerabilities. Edit the registry
HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Options\Mail
Add a DWORD of READASPLAIN=1
Now all messages will be displayed as plain text.

Schtasks is a command line tool that replaces the infamous AT command for scheduling tasks to run on local and remote computers.
You dont have to logout a user to run administrator installations. Shift+right-click the setup file, then select Run As and enter an admin username and password.

Rainys has some nice apps at http://vapaa.dc.inet.fi/~rainy/index.php including a skinnable desktop calendar and a performance meter.
SysMetrix is a cool skinnable clock and metering app from Xymantix at http://www.xymantix.com/
Another cool addition to your desktop is Desktop Sidebar from http://www.desktopsidebar.com/
Samurize lets you create your own cool desktop tools at http://www.samurize.com/modules/news/

Rather than modifying your Windows interface, you can completely replace it.
Litestep is one of the more popular Windows shell replacements from http://www.litestep.net/ You have to register at the site to access it.
Talisman Desktop is available from http://www.lighttek.com/
And Aston Shel is from http://www.astonshell.com/

PatchXP patches Windows to let you use non-Microsoft themes

http://www.belchfire.net/article205.html
tgtsoft sells Style XP
http://www.tgtsoft.com/
An easy tutorial on modifying your boot and login screens is at http://www.extrememhz.com/winxpcust-p2.shtml
Some cool themes available from http://www.lightstar1.com/ complete with FAQs on how to install them.

Wincustomize has a huge collection of skins for WindowsBlinds, WindowsFX and DesktopX, as well as skins for specific applications like WinAmp and CoolPlayer.
http://www.wincustomize.com/
ObjectBar from Stardock is a commercial app containing a number of tools for completely customizing your Windows. It contains apps like DesktopX which lets you download or create your own desktop [...]

Annoyances.org has a list of simple modifications you can make to Windows yourself at http://www.annoyances.org/exec/show/category02
An easy one to avoid unsightly gray rectangles around the titles of your desktop icons is to open System Properties in Control Panel, choose the Advanced tab, and click Settings in the Performance section. Turn on the Use drop shadows for [...]

The basic Windows XP installation looks a lot nicer (or worse, depending on your point of view) than earlier Windows versions. But you aren’t limited to the basic themes that come out of the box. You can modify the styles yourself, or download applications that let you install themes that others have created.

TqcRunas from http://www.quimeras.com/ can be set up to let users run applications with administrator rights. The admin password can be encrypted for security.

An excellent set of batch files for removing all the fluff that comes with Windows XP at http://jdeboeck.msfnhosting.com/ [Edit: this site is no longer available - but the forum thread is still available at msfn.org]
Use one of the methods on msfn for making an unattended installation CD and you’ll have a quick install and [...]

Click Start, click the Run command and type REGEDIT in the open text box. Click OK. This opens the Registry Editor. All the usual precautions for editing the Registry apply.
Browse to the following location in the left pane of the Registry Editor:
HKEY CURRENT USER\Control Panel\Keyboard
In the right pane, right click on InitialKeyboardIndicators and [...]

Add /sos to the line that boots your OS in boot.ini

[boot loader]
timeout=5
default=multi(0)disk(0)rdisk(0)partition(1)WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)WINDOWS=”Microsoft Windows XP Professional” /fastdetect /sos

To remove MS Messenger run the following command:

RunDll32 advpack.dll,LaunchINFSection %windir%\INF\msmsgs.inf,BLC.Remove

If you are a Windows network administrator I recommend that you set the WSH options to run scripts at the command prompt by default. The default WSH script host is Wscript.exe, which runs scripts in the GUI — this means that all input and output takes place in popup message boxes, which require user intervention [...]

To take full advantage of the power of scripting, your workstation should be running the most current releases of VBScript, WSH, WMI and ADSI available for your version of Windows.
Check that you have the latest versions at Microsofts Tales from the Script