Even XP Home will do the job, as long as you don´t want to join a domain ^^
The 64 version is incomplete, I can´t recommend using it.
CPU: AMD!! Faster for your money! (socket 939, 3200+ or better 3500+)
RAM: 1 GB for "normal" use, 2GB for Battlefield 2
Board: the Abit mentioned up there is ok ^^
GFX: yop, geforce 6600gt and above (I´d recommend a faster 6800gt
)
HDD: I love Samsung, not the absolutely best in performance (but up top) but very quiet