Hello Mark from Inverness ... and Welcome!
Like Grant, I doubt you would find happiness in that direction. USB 2.0 generally does not work with OS 9 on a beige G3. Try OSX on a G4 for better results with USB 2.0
I have had excellent results from Orange Micro USB 1.1 / firewire cards: at least six with nary a problem. I've also used several Macally cards - and Keyspan, Belkin, and generic Brand X - without problem. eBay is a great source.
The most important part of installation is remembering that you have to re-install the Operating System to get the Mac OS installer to "see" the USB card physically installed in place, and to "see" the need to install the proper USB drivers and support extensions. Easiest is to perform a clean re-install from an orange-9-on-a-white-label retail, full-install CD, which will leave you with a brand new System Folder complete with the proper USB drivers and support extensions and a "previous system folder", from which you will have to drag over all your favourite applications and documents, &c., &c. to the new folder. A custom install of extensions, and an install using "Tome Viewer' utility, are also possible, but they still require the same white label Mac OS 9 install CD - a grey label model specific install CD cannot be depended upon to install the correct extensions.
(If you don't happen to have such an install CD, you can get one - either 9.2.1 or 9.1 - for about $50 from applerescue.com or other fine Apple reseller. eBay is not a real good source because you have to wade through a long list of grey labels, copies, exact copies, burned copies, and "sure to work" copies (that don't), wait to win the auction, and then discover that you paid more than applerescue wanted in the first place. (eBay is great for other stuff, but not install CDs)
The hardest part of the installation is to figure out how to open your case, remove the PCI slot cover with a screwdriver, and press the Peripheral Component Interface card (your USB/firewire card) into its waiting slot (firmly), and close the case.
You may now perform the clean re-install, your Mac OS 9 installer CD will automatically "see" the need for USB drivers and install them as part of the process, and you're in business.
Similarly, use your ethernet port for broadband, and leave USB alone - it's too slow. Your ISP provider should be able to walk you through the installation. The only thing you may want to figure out ahead of time is how to set AppleTalk to the printer port so that the ethernet port will be available to the TCP/IP protocol. (I think I have all that straight!)
If you have any trouble, call Grant.
Regards ..... Jon