You would probably want a quad core since you'll be doing some video editing. The LGA 775 socket is a dead-end, though. AMD offers better components in that price range. Their integrated graphics are also considerably better than the Intel ones.
Yes you should consider an AMD build. Shortstuff linked a good suggestion that will serve you better. Quite often Intel is the better choice, but here with your needs you cannot beat the AMD onboard graphics or the MB price.
I wouldn't even mess with LGA 775 stuff anymore. Get yourself one of the LGA 1156 processors. If you have a microcenter nearby, you can get an i7 860 for $229 or i5 750 for $160. Whatever you do, avoid AMD. Some have argued that AMD is better performance for the dollar, but with the release of the Lynnfields, Intel has taken that away from AMD. The Phenom II X4 965 ($245) doesn't even come close to out performing the i7 860 ($229). Ram and motherboards cost about the same for both platforms.