I have three Linksys wap54g v1 produced in the far 2003 with 1.06 firmware onboard, ok they are old crap but they are still working pretty well and with the firmware update they get the wpa2 support. Latest firmware available for Linksys Wap54g v1 is the 3.05.03.
Clearly the Linksys’ support page doesn’t give nothing but i found good files anyway. You can download them from here.
For the upgrade you have to log inside the access point, the default ip is: 192.168.1.245 with credentials: admin: blank password: admin, and click on the Help button at the top right of the page. Once finished updating, the access point needs an hardware reset using the button behind it.