Mobo died. can get free one, and CPU, but only 2 DIMMS, and I only have 1gb ddr2 sticks. The PCU is more than enough, as is my dedicated GPU. Will 2gb be enough for a it Windows 7 instll to run XBMC well enough to view 1080p? I assume i'll be forced to revert to 32-bit, but I'm sure that'll be fine.
That's cutting it close for win7, especially if a jntergrated GPU is to be used. Have you thought about using openelec or xbmcbu tu?
Edit: just saw that you have a dedicated GPU - 2gb should do, but make sure to keep extra running programs to a minimum
2gb will be enough just don't run too many other programs while using xbmc, like teeedubb said.