Hey Michael,
One of the "safer" ways to do this is to avoid hardware RAID configs and use software raid. So you get get 2 x 1Tb drives and set them up in a mirror raid volume.
I would also recommend keeping the OS and the RAID drives (or partitions) seperately, so you can move the raid volume to another PC in case of catastrophic hardware failure (and not worry about a hardware RAID container / volume :)
If you are going to do windows, just plug the disks in and set them up as a dynamic volume and choose mirror when you create it.
Basic Storage Versus Dynamic Storage in Windows XP
http://support.microsoft.com/kb/314343
How to create a mirrored volume on a remote Windows 2000-based computer in Windows XP-based computer
http://support.microsoft.com/default.aspx?scid=kb;en-us;307880
Linux, by nature, is a bit more complex
Managing RAID and LVM with Linux (v0.5)
http://www.gagme.com/greg/linux/raid-lvm.php
Setting up software RAID in Ubuntu Server
http://advosys.ca/viewpoints/2007/04/setting-up-software-raid-in-ubuntu-server/
If you can't get or don't have dedicated OS drives, you can at least create smaller partitions for the OS on one (or both) drives, say 15~20gb, then use the remainder for the data RAID.
cheers