did you try a google search? or
http://freshmeat.net ?
Look at the UPS readme
http://www.tldp.org/HOWTO/UPS-HOWTO.html and also check out NUT, Network UPS Tool,
http://www.exploits.org/nut/.
There are other tools besides NUT, but I feel NUT is most popular.
There's plenty of documentation on the specifics of implementing the system.
--Kervin