I'm fairly fortunate, my Pentium 233 has one of the last generation socket 7 m'boards; an FIC VA-503+.  It supports UDMA-66, PC-133 RAM, up to 512 Mb.  Without flashing the BIOS, I can upgrade to an AMD K-6 450 Mhz processor.  Without a RAID card, I've had 3 IDE hard drives running.  It's an AT-style board, but I've got an AT case that'll allow up to 6 H.D.'s internally, and2 more in the external 3-1/2 bays- that's not even counting the 5-1/4" bays (4).  Since it'll be a server, I won't be dong much upgrading, once the thing's up and running.