Zog: another limitation of NT4 is security (and the lack of updates/support from MS, so the existing security holes will be there forever). Plus IIS is a royal pain, IMO. I think the Fedora setup will let you setup RAID5 during the install if you want, and Apache is fairly easy to use, especially for a single hosted site.
edit: the RAID5 I'm speaking of is the software sort.
also, samba works very well, considering it emulates a very messy, fussy, vaguely-specified protocol
colintheys: RAID5 is very CPU intensive; if you go that route I would strongly suggest a controller with a built in XOR engine, like those listed above.
Then again, you could buy one more 120GB disk (I'm assuming your first three are similar/same in model/performance) and setup a RAID0+1, probably cheaper than buying the fancy controller. You would see a small CPU hit, but nothing too major. OTOH, you would be locked in to that 240GB capacity, unless you later replaced all 4 drives, or got the updated controller.
If you get a different controller, you may be able add a drive on the fly later (depending on SW support, I think the 3Ware cards allow that), and merge it into your existing RAID5 to boost capacity.
hope that helps