I have good news! I just successfully got my iBook G3 (running OS 10.3.9) online using the Belkin 802.11g USB wireless adapter (F5D7050). I purchased it for about $30 at Circuit City (and they have a good return policy if you can't get it to work) and followed glad's instructions (thanks!). Here's what I did in more detail, in case there's anyone else like me who has no idea how to do this kind of stuff:
1. I downloaded the driver from the Ralink site (link provided in glad's reply). I used the one listed under Macs for chipset RT2500 for Mac v. 10.3.x (since that's what OS I have). I also tried the RT73 chipset driver, but it didn't work. I have no idea what a chipset is. It was no small feat downloading this driver since the whole reason I'm going wireless is that my ethernet port is shot.
2. I restarted my computer.
3. I put the USB adapter into the USB port. Then I opened my wireless utility, which is located in Applications. I clicked on "site survey" and since more than one router showed up (probably the neighbor's), I chose the one that corresponded to the router in my house, which is a pc wireless router, by the way. Once the proper router was highlighted, I clicked "add profile." Under "profile," I highlighted the router and hit "activate." A drop-down menu appeared at some point and under "system configuration" I chose "Network type" = 802.11 Ad Hoc. Under "Authentication & Security" I entered the network key for our router (you'll have to find these numbers for your own router somehow- my roomate gave them to me). (I can't remember what order I did all this, but you can probably figure it out.)
5. In System Preferences, I went to Network, and when I did the system notified me that there was a new connection detected. I verified that, hit "apply now," and things were good to go.
Hopefully wireless will continue to work! I will let you know. Good luck-
Melanie B.