I think there's not much point in spending 1500$ on PC.
You should be able to make something nice more in 800-1000$ range.
I'd suggest:
core i5 750 cpu
MSI GD55 mobo
2x2 GB of RAM (rated for 1333 Mhz or faster)
radeon 5850
small Intel 40 GB SSD for operating system and either Samsung F3 500 gb or Caviar blue 640 GB hdd for rest
OCZ 600W modstream or Corsair 650W PSU (even 600W is overkill but let's play it safe)
PROUD MEMBER OF THE PSP RPG FAN CLUB