my experience with servers of virtually any kind is that ram and disk io are the primary considerations. look around at ebay for a good used raid controller (i've seen hp and compaq controllers going for ca. $40) get a box with a big case (or assemble one yourself) and load up with as many scsi drives as you can that are a generation or so old. though there shouldn't be any trouble with name-brand controllers, you may want to double-check compatibility for your own peace of mind if nothing else.

if you don't want a raid controller, you can still gain the benefit by buying a good scsi controller and configuring software raid. this can be done very easily in the redhat setup. whether you choose hardware or software raid, i'd suggest configuring with raid 5, so if one of your drives were to go down you can easily rebuild with the parity information.

i'd also consider looking into a dual-processor motherboard. you don't have to be looking at dual xeons, but you'd be surprised at how responsive even a dual pentium pro with a lot of ram and a raid array can be. if you have the requisite knowledge to assemble your own box it can be done inexpensively. i picked up a gateway dual p2-p3 server board with dual scsi channels from www.compgeeks.com for $50 a few months ago. getting a case to fit it in is another story, but that's beyond the scope of our current concern. ;->