Weelll, you can't always believe everything the man at the computer store tells you (cf. Intel marketting strategies), and if this is the guy who sold you the puter, you should beat him about the face and shoulders until he repairs his product. Telling you just to go find that download somewhere is not on.
That said, there are a number of rumoured and perhaps a few real software issues with AMD and Windows, but which one are we trying to address? That's why I suggested we find out why your computer is rebooting.
Another good source is the ever-wakeful geek-corps at the forums of amdmb.com. If you pick the forum section that corresponds to your mobo manufacturer, they will tell you much more than you could possibly need to know about what the problem is. That said, they're an enthusiastic, helpful bunch.