The OrangeMicro USB2/FW combo card works well in a 7200 with OS 9.1. It should be supported from OS 8.6 on. It is even possible to install a well running OS 9.2.2 on older PowerMacs to have the most recent driver software (use OS9helper). I have tried this with a 7200 and a PB1400 successfully. I found a cheap USB host adaptor (not Mac specific made) working on a beige G3, but _not_ on a 7200.

As Bunsen said: USB2 functionality is not given on system software pre OS X, no matter what the host adapter is capable of.