Grats!
Which is why I still run XP PRO on my gaming rig.
Sounds to me like a video driver issue. Try rolling back to an earlier video driver if you are running the newest one. Maybe the card is heating up. Also make sure you load the latest winblows direct X driver package, if WIN 7 don't include it.
Also, try disabling any antivirus, or other security software you might be running on top of WIN 7.
I'm sure others will chime in with other fixes if this don't help, but I'm on heavy medication ATM, and this is the best I can do for you now.
Good luck.
I find that statement about XP amusing and wrong with regards to 7 ,Win7 will game just as well as XP,infact I have not used XP for over 3 years+ for gaming(I have even removed XP from all my PCs) and yes all my games run great on Vista and Win7 x64,including old 16 bit games via DosBox.
Getting back on topic install latest DX9.0c from here
http://www.filehippo.com/download_directx/ ,update your video card drivers too.
You don't say if this is a new build since it could be a hardware issue with a faulty product,make sure nothing is overclocked.
Some games you need to run as admin and XP compatibility mode,easy to google which ones,info here on how to run as admin and xp compatiblity mode etc..
http://www.howtogeek.com/howto/windows-vista/using-windows-vista-compatibility-mode/
Don't forget game patches too.
One last thing check your games and if they use TAGES or any other copy protection you may need to download latest version from their website.
Try a different video card if possible after you have done the above to rule out faulty video card.
I had a faulty video card that would play some games(years ago) but not all,simple replacement of card fixed the problem in my case.
Btw its always worth checking/testing your ram ,leave no stone unturned as they say.
It can be a pain game troubleshooting ,believe me I have done my share even in XP,but its worthwhile in the end with the experience and knowledge you gain.