Lookup the exact type of the USB device, then do some Googling. Perhaps support is already present in the current 2.6 kernels. Then you would have to recompile the kernel with support for the device (which at the moment is not very straightforward on PS3).
If you want to save lots of time and have some money to spare, my advise to you is to buy a Wireless ethernet bridge. This is a device that basicly makes wired devices wireless. It plugs into the ethernet port of your PS3 (the one that IS supported
). Example:
http://www.linksys.com/servlet/Satel...=8253087090B09
I've tried lots of things to get my PS3 wireless going (including a wireless USB stick) and ended up buying the WET54G as linked above.
When a proper driver comes out for the PS3's native wireless interface I'll use that instead.