hi,
definitely check out the quickertek company - they make all sorts of 802.11n products for basically all lines of macs, including pcmcia cards for old pbooks. their website is -
http://www.quickertek.com/ and the card i'd recommend for you is the nquicky -
http://www.quickertek.com/products/nquicky.php
i have the cardbus adapter and it's working great and has been incredible thus far. really nice people, too.
take care,
chris m.