Okay, stop right there.
Why would you buy that Dreamcast from your friend? It doesn't have everything you need to play games on it. Actually, let me correct that...
IT DOESN'T HAVE ANYTHING YOU NEED TO PLAY GAMES ON IT!
No cord, no controllers, no A/V cables, no memory cards... in other words, it's a gray, useless box right now. And to top it off, you don't even know if it works. If you're going to buy a Dreamcast, go to eBay, and find one that has all the required equipment it needs. By the time you get done searching for and buying the missing components for the one you mentioned, you'll have spent the same amount you would have on eBay... possibly more. Once that's accomplished, then start looking for games. Speaking of which...
AirForce Delta (Flying)
Alien Front Online (3D Action)
Bangai-O (Shmup)
Border Down (Shmup) *
Capcom vs SNK (Fighting)
Daytona USA (Racing)
Dead or Alive 2 (Fighting)
Draconus: Cult of the Wyrm (3D Hack 'N Slash)
Fatal Fury: Mark of the Wolves (Fighting)
Giga Wing (Shmup)
Giga Wing 2 (Shmup)
Grandia II (RPG)
Gunbird 2 (Shmup)
Last Blade 2 (Fighting)
Last Hope (Shmup) *
Mars Matrix (Shmup)
Marvel vs Capcom (Fighting)
Marvel vs Capcom 2 (Fighting)
MDK 2 (3D Action)
Metropolis Street Racer (Racing)
Red Dog (3D Action)
Resident Evil 2 (Survival Horror)
Resident Evil 3 (Survival Horror)
Resident Evil: Code Veronica (Survival Horror)
Skies of Arcadia (RPG)
Soul Calibur (Fighting)
Street Fighter III: Double Impact (Fighting Compilation)
Street Fighter III: Third Strike (Fighting)
Street Fighter Alpha 3 (Fighting)
Sword of the Berserk: Guts' Rage (3D Hack 'N Slash)
Test Drive Le Mans (Racing)
Test Drive: V-Rally (Racing)
Under Defeat (Shmup) *
Wild Metal (3D Action)
Zero Gunner II (Shmup) *
*= Japanese import
Anyway, those are my thoughts (and recommendations) on it.