Well, Honestly XP was the Last Version that I would ever use, but you must understand that using XP is dangerous as Security Vulnerabilities put you on risk of infection or hacking.
I faced this same dilemma at the Launch of Vista, after trying it out I formatted my machine and Broke the CD, so much hate for Vista. Windows 7 maybe faster but I haven't seen that, it just too much bloat for me. Where XP is too dated.
Might I suggest Linux to you? Try it goto LinuxMint. Expect a small learning curve, but it's one of those things once you go there you will never wanna come back to Windows, the plus side is, It's free and Open Source.
You can Download, Burn, and Load it, with out installing it. Basically When you boot it will ask you if you want to to try it, select the first option which will be to try it. And it will take a few minutes as it loads itself on to the RAM, and then it will present to you a slower version of the full fledged OS as it is installed. It is slow because it is being run from the CD, it isn't installed. You get to test it and if you like it install it.
If you are worried about games, you should look into WINE, alot of Windows Games run on Linux through Wine. You can see your application compatibility on WineHQ.com