Well it depends on how comfortable you are with opening up the computer.
There isn't really any guides on doing this, so I would add an external usb wifi adapter.
There's a really powerful usb wifi for $30 w/ free shiping
[http://www.newegg.com/Product/Product.aspx?Item=N82E16833166027]
It says it works with mac 10.3-10.6, so if you have that I recommend using this or another usb wifi adapter instead of an internal airport extreme card.