I have happened upon a slew of vintage Macs and am now selling them...

They are all PowerMac G4 towers of varying speeds... http://en.wikipedia.org/wiki/Power_Mac_G4
Expansion bays include: 4 internal 3.5" ATA drive bays, 1 optical drive bay, 1 Zip 100/250 bay, 3 - 64-bit 33 MHz PCI Slots, 1 AGP 2x Slot
Each tower can be expanded to 2GB memory and 128MB hard drive.
Memory: http://www.amazon.com/gp/offer-listing/B00006BA9U/ref=dp_olp_new?ie=UTF8...
120MB ATA drive: http://www.nextag.com/120-GB-hard-drive-ATA/compare-html

Actual models listed here:
1) 400 Mhz PowerPC G4 Tower, AGP Graphics, 10GB ATA hard drive (4.27GB available), DVD-ROM, 384 MB SDRAM, OSX 10.4.11, 2 Built-in USB 1.1 and 2 Firewire 400 ports, 10/100BASE-T Ethernet.
Serial Number: XB0156LQHSE

2) 350 Mhz PowerPC G4 Tower, AGP Graphics, 10GB ATA hard drive, DVD-ROM (fairly balky), 320 MB SDRAM, OSX 10.3.9, 2 Built-in USB 1.1 and 2 Firewire 400 ports, 10/100BASE-T Ethernet.
Serial Number: XB0042UTHM1