You'll need to be very careful about buying a RAID card for SATA or PATA. While I have no personal experience with SATA I have trawled through loads of posts regarding it, when trying to solve my IDE RAID problems.
My suggestion to you would be to buy 2 of the biggest PATA (IDE) drives you can and run them in RAID 1. SATA seems to be a bit of a sore point with linux at the moment. If you have on board SATA RAID and want to use that instead, check SME has built in drivers or you can find someone with exactly the same HW and a working driver disk. Otherwise, like me you could be wasting money on a RAID system you cannot use, or even worse be forced to use a Windows alternative.