I'm using a GlobalSat CF GPS I picked up at Semson's, but any SiRF standard GPS would work. CircuitCity carries AmbiCom's GPS which should work.
However, I've checked at the Billionton site and their GPS is definitely SiRF based and so should work.
Try this utility...
http://www.peregrine.com.my/tech/GPSInfo.zip and see if it can see the GPS. You might also want to make sure nothing else is tying up the port for the GPS.