I've done it using the AP card for a Mac Pro, and it only sets you back a little over $50. The AP card for the C2D MBP is different (three antennas) and will not work as well as the card for the Mac Pro.
Not a job for beginners, but if you're careful and take your time, certainly something most can do with patience.
A good time to swap out your hard drive for a bigger/faster one while you're in there...
MD