A USB 2.0 PCI card is what you need. Best bet is any card with a NEC PD720100 or PD720101 chipset (xlr8yourmac results recommend the same). Read this for more feedback:
http://www.xlr8yourmac.com/firewire/...eep_sleep.html
Stick with the NEC chip, and try NOT to use drivers, Tiger doesn't need the drivers.
All of these Cards are NEC chipset based
Adaptec 3100LP
BAFO BF-460
Belkin F5U220
GWC UC-160
IOGear GIC250U & IC251U
Keyspan U2PCI-5
O'toLink U2-C2A, U2-C2B, U2-P20N & U2-P50
Ratoc PCIU5
USBWholesale UII-PCIP
I just bought a used IOGear GIC251U & installed it in my G4 400MHz AGP. Works at USB 1.1 speed when I'm booted in OS 9.2.2 & USB 2.0 when booted in OS X.
Cheers, Tom