Just bought a used Powerbook and need a wireless card but which one ??

You have a second-generation Titanium Powerbook G4, manufactured in March 2002. Yes, you are in the right forum.

It's been two or three years since I checked around for third-party wireless cards for a Tibook, so these links are old:

http://www.sonnettech.com/product/aria_extreme.html
http://www.macwireless.com/html/products/wirelesscards/11g_11bcards/11gPCCard.php
http://www.macsense.com/product/networking/wpe800.html

I'm not sure all three cards are still available, but if they are, they will all work well in your Tibook's CardBus slot, and they don't require any third-party software.

Of course you could also look for a used original Airport card (802.11b, which is slower than any of the cards linked above). For a long time, they were absurdly expensive compared to the third-party CardBus wireless cards, but that has probably changed now. The drawbacks are slowness and, of course, the fact that they're only available used now.

Message was edited by: eww

...and the net says its compatible...

"The net" says a lot of things, and if you believed them all...well, you can see where I'm going with that. More important than what "the net" says, what does Proxim say about Mac compatibility for the card model you're using? Does Proxim offer a Mac driver for the card? I suspect it needs one, and if Proxim doesn't offer one, you'll have to find a third-party driver that works with the card. Others may be better able to advise you where to look for that than I am. My own inclination, were I in your shoes, would be to spring for a card that has been proven to work with Macs and with Apple's own Airport software, needing no additional driver.