The WLAN card in new core 2 duo MacBooks is unsupported by the current MadWifi releases. These cards are based on the pretty new AR5008 chipset family, which is not supported in the HAL of those releases.

However, there now is a experimental MadWifi version with a brand-new HAL that should work, at least for "legacy" functions (means: no 802.11n support yet). Read more here.