Trouble with new computer

Hello everyone. I just built a new computer and I've installed the drivers for the various components... yet when I go to watch YouTube videos, DVDs or play any type of game (from any era) I get intermittent choppiness that makes it impossible to enjoy anything.

I've got an

AMD Athlon 64 X2 6400+ at 3.2 GHz (newegg link)

2 Gigs of RAM

Asus M2N-MX SE MoBo (newegg link)

Asus Radeon EAH3450 w/ 512 MB (newegg link)

Sound Blaster Audigy SE

Windows XP MCE

Windows has drawing problems as well. I originally was playing UT3 with this and it worked smoothly and then would drop to 2 or 3 frames a second... back and forth. So I thought it was just too much for my setup. I installed UT2k4 and had the same issue.

I then tried Call of Duty (original) and same thing, as well as System Shock 2, Red Alert 2, C&C Generals and I tired The Sims 2 all with the same problem. I think I either have the wrong drivers for the video card or the wrong drivers for the processor but cant seem to find any alternatives. I have no unnessesary processes running while trying these games...

Hoping someone can help!

This isn't a virus. I've used three different operating systems (Ubuntu, Windows Vista and Windows XP in that order) and formated the HDD each time.

The problem is probably the video card.