Note! Everyone who understands what this does thinks the 900-AP hack is a bad idea. Have a look at http://www.maokhian.com/wireless/wap11.html for more details.
Firstly, you can get the 1.4j1 firmware from this page. Wap11Hack
Also the atmel snmp config utility which will allow you to adjust the output power. (see instructions on that page)
Also, the linksys wap11 USB config allows for individual tx and rx diversity setting which is handy if you intend to mast mount one of these babies! wap11sw.exe
These are much nicer config tools to use than the dlink versions!
FYI, the RP-SMA is attached to the 'Left' output. The 2 antennas are for diversity, as you can see the internal one is pretty lame, but you'll need to disable it for external links.
Vak suggested to me that the best way to do this was to remove it altogether and replace it with a resistor of something like 50 ohms. Don't leave it unconnected without the resistor as you may damage the output amplifier.