Interesting article on using Windows XP to do RAID-5 in software. I'm now using Windows XP to do RAID-0 and it's working nicely. I always thought it would be nice have an external RAID-5 box that connected using firewire so that it could be moved easily and connected directly to different machines. However, the problem with a hardware-based RAID-5 system is that if the controller dies, it's unlikely you can successfully transfer the array, intact, to another hardware-based controller. With Windows XP, it turns out to be simple to move the RAID-5 array to another machine.
So taking a quick look at Dabs, going this route you could install 1 Tb of RAID-5 into a file server for about £600. Add 1Gb Ethernet and you have a poor man's Storage Area Network (SAN).