From the information you provided I suggest you go to:
http://www.pandawireless.com/Drivers%20|%20Panda%20Wireless.html
The drivers only go down as far as OSX 10.4 but if you read the Macintosh manual linked at the bottom of the page they provide contact information, including asking you to tell them which OSX version you run such as "10.3".
I guess you could also just try the 10.4 driver if you can install it. Sometimes people only put the actual system version with which they have tested software but it may work on others, they just don't want to suggest it.
Which exact model dongle? It is going to take a lot of effort getting this thing to work, if at all and we need to know as much about it as possible. I got as far as discovering Ralink's website is down but found another set of links taking me to Mediatek's website with downloads to many products, including legacy items starting with "RA". The page taking me there though only started with Leopard OS and it is possible if this device dates from later than 2006 that the software requires an Intel Mac.
What Power PC Mac are you running, with what operating system?
I have an iBook G3, running OS X 10.4.11
I believe it's a Panda Wireless N USB receiver. I'll try to find the link to it again and send it if needed.
I found the link to the adapter:
https://www.amazon.com/Panda-Ultra-150Mbps-Wireless-Adapter/dp/B00762YNMG
ralink wireless utility for powerpc mac
