Still awaiting moderation...
Some people manage to make them work under OS 9. When I researched mine, it had a chipset that had worse documentation than cave paintings. Some super generic crapset with no drivers to be found. It's chipset is specifically listed as not-compatible with OS 9 in some thread somehwere explaining the best/worst USB Cardbus cards for PPC Mac OS & X. The linux drivers didn't work under MintPPC either, apparently no PPC support. I guess they have switched chipsets a few times for all these inconsistencies...
The firewire card is likely your better option.
To get to the HDD:
Pull out of the two tabs on the front of the computer. This will empty the two expansion bays. Then, feel around on the top inside of the expansion slot for a slider that can be pulled back. Pull back both of these and the keyboard will pop out. The HDD will be sitting to the right of the CPU.