They all seem to be Windows only

What Mac OS?

10.5

How old’s the mac that you need such a thing? (and why do you need it?)

I have a mini pciE wifi card that works in OSX from a previous hackintosh if that’s of use.

5 years old – no Airport card fitted and they are difficult/expensive to get hold of

http://cgi.ebay.co.uk/WIRELESS-USB-WiFi-ADAPTER-DONGLE-XP-VISTA-Windows-7-/110618060771?pt=UK_Computing_Networking_SM&hash=item19c159a7e3

An Airport card is only £20 or so. What Mac do you have?

The cards are cheap but the adapters are the expensive bits, or at least they are for G3 iMacs.

I had this a while back and ended up finding something on Ebay that worked. Unfortunately I no longer have it nor can I recall what make it was but they are available and they do work although I had no end of trouble setting mine up – it wouldn’t remember passwords so on every start-up or loss of signal I had to log back on to the software to re-enter lots of details. I eventually made it work properly but it was more by chance than design.