Why can’t I get any USB 2.0 PCI card to work?

I have a mirror door, dual G4/1.25 GHz, PowerPC running 10.5.8 (model identifier: PowerMac3,6) with 2 GB RAM (the maximum).

I’ve tried to add USB 2.0 capability to it since shortly after I bought it new. All the PCI cards that I’ve tried were designed to be compatible with the Mac G3, G4, G5 and Intel processors. My most recent attempt was with an IOGEAR model GIC251U and a SONNET Allegro, each of which has 4 external USB 2.0 ports and 1 internal USB 2.0 port.

I spent several hours with a Mac technician trying to get either the IOGEAR or SONNET card to work, but he was baffled and finally threw up his hands in defeat, not knowing what the problem is.

I have 3 other PCI cards installed, and they all work perfectly. In our attempt to get a USB 2.0 PCI card to work, all the other cards were removed, but still no success.

At this time the IOGEAR card is for auction on eBay for a tiny fraction of what I paid for it. The SONNET card is on its way back to OWC for a refund.

I’ve pretty much given up on this pursuit, but if there’s anyone out there who thinks he/she knows the solution to this problem, I’d love to hear what it is.