it'll run fine for gaming. but your really not going to see a huge difference compared to a normal gaming rig. just look up benchmarks for intel's skulltrail system. To the best of my knowledge serverboards and workstation boards are pretty much the same.
I would use vista ultimate x64 though, it's got much better support then xp 64. Also there are alot of new mainstream boards that will take 16GB of ram. also considering that nehalem will process 8 threads (using 4 cores) i would advise against this type of build unless your using some serious workstation type apps, like maya or 3d studio max on a professional basis.