When it comes to
VirtualDub, especially capturing, 1.10.x is not as stable as 1.9.x. And don't even bother trying to use the VirtualDub2 fork, it just gets worse.
You have to realize everything about analog video is chaos, and capture cards/software has always been just as fussy. Drivers frequently don't play nice, and conflicts are the norm. And while Windows XP SP1/2 was really stable, Microsoft was never a darling of stability.
The main system here sometimes boots and forgets the AIW part of the ATI card, so I have to reboot. And it's suddenly working fine again.
I'm not overely familiar with the ATI 750, aside from the facts that it has AGC issues. However, it's probably like every other cards in terms of adjustments, just use the levels on the
VirtualDub video menu in capture mode. But, more likely, any brightness/contrast issues are a flaw of the card, or a non-calibrated monitor (meaning the video is actually fine).