Before I went wireless at home, I used a IIci running NetBSD as my router / DNS server. Worked like a charm. The box fit under my desk and could run headless, so I didn't have to worry about it.

One option for file storage is to combine a bunch of old SCSI drives into a JBOD. You'd need a SCSI enclosure of course, but you could run up to 7 drives total and create one massive disc out of them. I've got a stack of old SCSI drives that I'm toying with for this exact purpose.