Any wireless B specification card should be fine. I personally recommend grabbing a USB unit as they tend to have better sensitivity for picking up distant access points. This is especially handy if the distances in your house WAP setup are going to be long and far apart.
See if you can't pick up a cheap Linksys WUSB11 card somewhere in the FS/FT forums. G cards will work fine too, but won't give you 54Mbps speeds; only the 11Mbps rates. Seeing as G is flying off right now, you might be able to get them cheaper than their B counterparts!
Good luck!