No sir that's not true. It's only legal to own a backup of a ROM if the original manufacturer says so (Amiga, Amstrad) and are running either a licensed BIOS file or one extracted from your own system.
Free Multiplayer
ioUrbanterror <---- Free counter strike with a lot more more actions. Cross platform, MANY ppl play this, RECOMMEND!!! you can play off-line with bots too.
Battle for Wesnoth <---- One of the best turn base strategy RECOMMEND!!!
Wolfenstein Enemy Territory <---- Free Battlefields, many pply still play this but so many sevr are full of bots.( I dont know how to add one)
Commercial
COD2 <--- use pc keys for 10 bucks?
COD4 <--- same? It's working all right but pc version rules
Enemy Territory Quake Wars <--- same? It's working all right but pc version rules
Unreal tournament 2004 <--- can be exspensive
Halo /Demo <--- super exspensive, Demo for free
Doom3 <--- Still exspensive
Quake4 <--- Still exspensive
Worms 3D <--- never try but they should work well
Spintercell <--- never try but they should work well
Dosbox <--- my personal fav
Wolfenstein
Theme Hospital
Theme Park
Simcity 2000
and your favorite oldies
Doomsday Engine<--- Doom engine games with updated graphics
Emulation
MAME OSX <--- STF3, JOJO, KOF
SNES9x
Kega Fusion
PCSX 1.6 intel pre alpha
Sixty Force
visualboy Advance
unofficial Cider port (works fine but multiplayer may not works/ untest)
*DONT ASK ME WHERE TO FIND THIS*
Farcry
Battlefield 2
Battlefield 1942
Battlefield Vietnam
Soldiers of Fortune II Double Helix Gold <--- can play multiplayer/untest
GTA Vice city
GTA SANS