You can now get Windows XP Service Pack 2 by going to Windows Update. This is probably the best way to update a single machine. Word of mouth is a great thing. Be sure to tell your friends and family to update their Windows XP machines.
Windows XP users: Get Service Pack 2 today
Your first step to help protect your computer is to install this new security update to Windows XP.
In related news, there was an XPSP2 story on NPR this morning. They interviewed Rich Kaplan and others about the service pack.
Fix Released for Windows XP Security Flaws
Microsoft rolls out its biggest and most comprehensive security fix for Windows XP. The company says the patch will make it tougher for hackers to break in.
Update: I added a better link with more options for getting the service pack.