If you have two 320-gigabyte hard drives in a RAID 1 array, how much disk space does Windows see?
Also, is it possible to provide RAID protection if the motherboard you're dealing with doesn't support it?
Two 320GB in raid 1 is the same amount of usable space as a single normal 320GB drive.
You can do software raid in linux, but not windows*.
You can however buy a RAID controller card. This not only generally provides better RAID performance, but means you are no longer tied down to using the same motherboard with your raid set up. Good cards are generally expensive, but a 2 disk RAID 1 shouldn't set you back much.
*Ok, there's "dynamic disks", but they're a little different and I personally wouldn't go near them.
XP took, iirc, about 4GB. Vista and Windows 7 take about 6, but grow larger over time.
Raid 1 uses the two drives for mirroring, to increase redundancy and read speed. Everything you write to one drive is mirrored on the other - windows will see 320GB.