I use them for my game. Just rename you .md3 to .mdl if you dont wanna go into qc and change the file names. Nothing more then that, texturing is another part.
I'm struggling to get .md3 map models working. I've set them up in qc as per .mdl map models, but they don't show up. I've renamed them .mdl and tried leaving them as .md3, but no luck. (I'm using DP, obviously.)