putting all your media on the one drive/partition will be fine, yep. It's just about organisation. Whatever works best for you.
It's best to have all that stuff on a separate drive from your OS, but i'll assume you knew that.
your ATI card will be fine for capturing from vhs. I don't know how UVS8 is, i've never used it, but if you have it, you'd be as well using it. If you find that it has limitations that hinder what you want to do, then upgrade to something better.
I'm fairly sure there'll be a topic already posted that will tell you how to do this. Happy searching!
