In most cases you want 4-8 Gigs of ram, and 2-4 cores in the cpu. The higher clock rate the better. Going beyond 3.4 GB of ram requires a 64 bit os. Once you hit 8 gigs of ram, start spending money on a SSD.
*Most* computers don't *need* more then 3-4 cores, assuming windows and the video chews up 1-2 cores (peak) that leaves 2-3 cores for everything else. Unless you are going nuts with multi threaded software, or only have 2 cores, turn hyper threading off on Intel cpu's.
The machine I am sitting in front of has 64 gigs, and 6 cores. I am currently bouncing between 7% and 13% cpu, and using 6.2 Gigs of the ram. Task manager says 2 cores are 0-1%, 3 of the other 4 are bouncing between 5-10%, the last one is actually doing some work. I also have a 480 gig RVD3X2-FHPX4-480G. This disk is beyond stupid fast. I routinely benchmark 1.2 Gig / second rear and .8 Gig / second write.