if you're doing photo and video mainly, i'd check out the p4, in most
benchmarks the p4 takes the lead. Check for benches on the relevant program you plan to use.
If you're going mostly editing, going dual cpu would benefit you more so than dual video cards. Xeons or opterons, just look for benches in software you're planning to use.
high powered cards can easily play todays games at 1280x1024 or 1600x1200 with most if not all quality options on.
If you're budgeting, for $200, the 6600gt, for $300, the ati x800xl, i wont bother mention the gt at 400 because it's about on par with the 800xl and $100 more. then you have the really high end stuff, which isn't going to make too big a difference over the xl. If you have to get the best of the best though, the x850xt..
edit - damn, ati bumped the price to $350