Depending on your situation, it may be a *very* good idea to switch from Windows XP to Ubuntu.
The advantages are: Software Freedom, low cost of operation. Can co-exist with Windows. Great way to learn UNIX. Underlying philosophy is very aesthetic and liberating. Can be whatever you want it to be (router, TV recorder, web kiosk, multimedia production machine, etc.). You can run virtual machines to run the Windows OS if you need that software. Completely free, automated OS upgrade every 6 months if you want.
The disadvantages are: Cutting-edge hardware may not be recognized properly, Windows software may not work in WINE. Cannot buy off-the-shelf software and hardware without doing some Googling to see if it's compatible.
There are popular games that work with Ubuntu under Wine, and you can check the Wine compatibility database for that:
http://www.winehq.com
As for software, I found that everything I needed as a professional web designer and illustrator already existed under Ubuntu. To top it off, there are many features and conveniences in the desktop that are much better than those found in other operating systems. It's nice to click "upgrade" and have all your software, not just your OS, upgrade itself.
Once you are feeling advanced, you can start using the command line for some tasks and realize why nobody (not even Apple or Microsoft) has abandoned it after all these years.
You can also experiment with different versions of Ubuntu on the same machine - I have Kubuntu and Ubuntu Studio both installed here, and I just select which one I want to use at the login window. I'm posting this from Kubuntu.
Windows users may have a hard time adjusting to the software install method in Ubuntu. Instead of surfing to a website and grabbing an installer, you check in your package manager first, to see if your machine can auto-install for you.
A good way to start out is to pick up a new hard disk and install Ubuntu on that. This means you get to keep XP while you adjust to the new interface.
Since a new version (Gutsy Gibbon) is being released in October, you may want to wait until then to try out Ubuntu.
Whatever you choose, good luck!