Will,
are there open source 3D fighting game?

Sure, try googling it. You may have a look at Dariusz Maciejewskis master thesis project: http://code.google.com/p/fighter3d/

Fighting games are a lot about timing. You will need lots of timers, a system to recognize combos and maybe keyboard chords.

A lot of effort is put into the graphics these days, but I'd advise you to start very small - you could start in 2D or even in text mode to get the underlying systems working.