RAID 5 all the way baby...
I bought a silicon image pci raid card that does RAID 5 for about £20 (see below for example)
http://cgi.ebay.co.uk/Silicon-Image-...QQcmdZViewItem
It takes 4 sata 150 drives and is recognised by windows without having to get drivers from the website (which are available if you need them)
4 x 250Gb sata drives gives you about 750Gb of storage. The resaon for the loss is that with RAID 5, if you have a disk failure, you can swap out the faulty drive, do a rebuild (very easy) and job done. No data loss...
The best thing about these cards is that if you have a system failure (my motherboard blew up in December!!!) you just plug the card into the new motherboard and away you go... NO DATA LOSS...
There are other cards available (check out the XFX raid 3 card which is similar, but is meant to read/write quicker and takes sata 300 disks), but for price and ease of use I don't think you can go wrong.