as I told on the FAQ, pretty much all based usb dongles based on ralink chipset support either powerpc mac.
About linux, yes they support linux too, about powerpc linux, I don't know, but I guess it will do.
Almost every cheap usb dongle on ebay has ralink chipset.
Asus and SMC make them too.
I agree. Many of the Ralink chips are compatible with PowerPC.
When my Airport card crapped out, I got a cheap WiFi dongle with a Ralink chip on eBay. The only problem I had was that it came with a mini-CD to install the driver, which I wouldn't put in my iBook's optical drive. I spent a good deal of time searching for a site on which I could download the driver instead.
During my search, I stumbled over more than one post in which it was stated that the drivers that came with the dongle were not for PowerPC with OS X. I later confirmed this by inserting the mini-CD in a friends tray loading drive.
After a time, and when I was out and about during the blackout following hurricane Sandy, I noticed that I wasn't getting very strong signals from the dongle. So I bought a USB WiFi Signal Booster, also with a Ralink chip. I again had to search for the driver. I'd learned from my original search that I needed to track down the driver based on the chip (Ralink 3070), and not on the name of the dongle. It was a quick search, and I now get extremely strong signals wherever I go compared to the original dongle and the AirPort Extreme card.
As a bonus, where I live the cable companies piggy back on each other's WiFi networks so as to provide more widespread coverage. I don't even need to sign in to the other cable providers' WiFi networks -- the system works automatically.
So now I have a WiFi signal booster that works incredibly well, and a backup in case these cheap Chinese products fail. I paid a total of $17 for both.