Yeah, USB would probably be the way to go. I only have 3 PCI slots, and they are taken up by am audigy, Geforce 2, and an ATA/100 controller. I put in a 10mbit isa nic, but it sucks. It's especially a pain when i need to transfer files between computers.
I'm thinking of getting a USB nic myself. ISA suck. If you had a couple ISA slots, you could always bridge a few isa nicks, but again, it's ISA. YAY usb