Locking up with movies...
I had this problem with my D470K (M-tech's version of the 4750). If I tried to play a movie (from a DVD or file), the player software would definitely lock up, and would often lock up the whole machine. I couldn't start WCIII either, since it always begins with an intro movie, and the machine would always lock up. I spent a week installing all the different video drivers and trying different things.

I talked with tech support (Pro-Star handles M-tech's support), and the guy told me to re-install XP, and install the drivers from the CD *exactly* in the order given in the manual.
I rolled my eyes

, since I *obviously* know what the heck I'm doing, but did it anyway under the theory that if I followed his instructions and it still locked up, I might have grounds to return it, or get further, actually helpful support.
Well guess what, I downloaded all the latest drivers from Pro-Star's web site, installed them in the exact order specified in the book, and the problem went away.

I don't know which driver I installed that caused the issue, but I've since installed SP2 with no troubles. I do get the DVD "stutter" issue if I try the Catalyst 4.9 or 8.07 beta drivers, so I'm just sticking with the older drivers that I got off Pro-Star's site until ATI fixes the problem.
Thus far, the only driver I've updated is the AMD processor driver from AMD's site, and everything works great.
Also, if you haven't already:
Install MSN messenger 6.2.
Go into the Camera Settings, and click on the "Advanced" button.
There should be three radio buttons under a "No Flicker" heading: Off, 50Hz, and 60Hz.
Set this to "Off". Your camera picture should brighten up drastically.