50 gigs should be fine then, then again, thats also depending on how many games and videos you're talking about. Movies will run at about 500-700 megs. So 2 of those and you're already pushing a gig. Most games are getting close to about 3 gigs. So it all depends on how much of what you're going to have.

If 50 gigs isn't enough, you can always add another harddrive later if you have the money to spare.