FOUR THOUSAND DOLLARS? OMFG....
Man.. The possibilities are endless, you can get the best of the best of the best. But really, after about 2000 dollars or so, the improvement is really not worth the price. Basically, around 1500-2000 is the best price
erformance ratio you can find. But 4000 is a very high budget to spend on computer parts and whatnot, but if thats what you want, I guess thats what you want :P
I'm not gonna make you a build, because lots of other peopl ehere will. Probably dual core processors, SLI video card, SCSI harddrives, oh man :P