All of Cisco's base station models are EOL (end of life), which I presume is why it has been about a year since the last firmware release for it. Cisco's Base Station supported PPPoE and DHCP Server mode, but did not support roaming or LEAP. It only supported 10 simultaneous users when set to AP mode. Hence, it had more in common with the inexpensive D-Link, LinkSys, and NetGear APs carried by Best Buy and Circuit City that a Cisco AP.
Cisco's Base Station was physically, as well as functionally, different than a Cisco AP:
1) AP has console port, BS did not.
2) AP has two antenna connectors for diversity, BS only had one captive antenna.
3) The BSM version of the base station supported an internal modem, the AP does not.
I never tried loading an AP image onto a BS. My best advice would be not to try it unless you know of someone who was able to do so successfully.