I may not have the EXACT setup, but I have a RAID 0 array on 3 x 80GB SATA drives by HItachi (by the way, they are pretty damn fast). I have my OS, apps, etc, all on C and I've got another partition on D that just stores temporary data files until I offload them to my file server.
I know it's risky business, especially on RAID 0, but if you don't care about loosing your data, then I say get a RAID array on multiple drives (I think 3 SATA drives is an ideal number. I've ran HD tests and it seems that on a SATA 150 bus, 3 drives will almost but not quite, saturate the bandwidth....with 4 drives, the bus is filled to the brim and with 2, there is more bandwidth allowed for another drive.....)
Anyhoo, as far as performance is concerned, partitioning really won't show much difference on one drive.....just my two cents, take it or leave it.
TTFN