Just get a Motorola WPCI810G PCI card.  It's got a standard antenna unlike those on apple airport cards.  The first one i got was around $25, when the one I got last week I won on ebay for $9.99 (+$8 shipping).  it's true plug and paly too, no drivers needed.
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"Tuesday's in the 80's?  I was in bed by 8... ...and home by 11.  OH!" -Quagmire
http://emax4.fortunecity.com