Hello,
I've also found it difficult to replace the wireless card in my Macbook Pro. I was able to track down the current part number in my device as being 661-3890; but I figure it may be better just to upgrade to an 802.11n compatible card. I've found a few listings on ebay but they are not straight forward. I want to make sure that anything I might buy is at least compatible with my computer.
A creditable site, OWC, has a part number 661-5048 they sell that is compatible but is on the upper end of the price spectrum. I have the A1150 Macbook Pro (1,1) which I believe is also referred to as the late 2006/early 2007 model. In my research I was able to deduce that some people have had success replacing their cards with the Atheros AR5BXB6 card although there appears to be some debate regarding the different Manufacture Part numbers (482261-001 and 482261-002). There are a few of these listed on auctions (used and new) but the range in price is $100.
I'm new to the Mac screen and would appreciate any help in the right direction as I have yet to find an authority that confidently and clearly states what cards are compatible with my box. Thanks!