Make sure you buy the Firmware developer kit to program your ap121, you will also need serial to USB.
http://www.data-alliance.net/servlet/-strse-710/Developer-Kit-for-Hornet-dsh-UB/Detail
Or you could buy the ap121 with open wrt on it.
http://www.data-alliance.net/servlet/-strse-667/Alfa-AP121U-802.11n-AP-fdsh-Router/Detail
I had bought the ap121 with out open-wrt on it, so I had to by the developer kit to program it.
Data Alliance is a great US source to by from, have not had a problem with them.