Depends on type drives (SATA/ATA) and RAID config (0,1, 0+1, etc.) you plan.
If all drives are SATA, then take two 80gb drives and plug in to SATA for
RAID 0; then use SATA to ATA converter and attach 120gb drive to ATA
connector. Vice versa if all drives are ATA.
For what I see as far your plans, you've no reason/way to go RAID as your 2
80gb drives will show as one drive in RAID 0 which means you can't seperate
OS on one, then music on other.
Besides RAID 0 is not very secure and not particularly fast (vice RAID 0+1,
but that requires 4 similar sized drives).
RAID info:
http://www.storagereview.com/welcome.pl/http://www.storagereview.com/guide20
00/ref/hdd/perf/
{click to "Summary Comparison of RAID levels" if you want brief overvies}
http://www.acnc.com/04_01_00.html {Summarizes RAID 0}
With the drives you've got, I'd suggest stay out of RAID. Otherwise, if
deadset for RAID: 120gb for OS, the RAID 0 for 2 80gbs (store all AVI/music
there, but only 80 gb avail tot).
Good Luck!