Seems that many of the newer Broadcom mini-PCI (and I guess therefore PCIe) 802.11 cards, especially 'n' versions with low power chipset and often BT on same card, just don't work on Snow Leo, even though they did on 10.5.8, as stuff in OS X that enabled compatibility is dropped as other newer cards are supported.
There's tons about this on all the netbook forums...Won't quote part numbers here, as there's various ones involved, but a quick google should give you lots of info.
Basically, if your card is not working either OOB or with a simple device-ID injection to the Info.plist, then usually you are out of luck and need to get a new card.
Conversely, if your 'n' card is working, then it's often worth re-flashing the card with alternate IDs to get additional speed performance by having the card be seen as an Airport one, rather than 3rd party.
