The drivers are on SlackBuilds.org. I have an APC Back-UPS ES750. ( its usb attached ). The apcupsd driver for me works on Ubuntu 10.04 on my netboook, but not on any OS ( Ubuntu 10.04, Mandirva 2010.1 and Slackware 13.1 ) on my main system. Just a word of caution. The doc is good enough, you will find it here -->http://www.apcupsd.com/
I have been beating this thing to death for 6 months. My main system never creates a device, no matter what I do. I know the APC ES750 is O.K. since it works on my netbook. The power supply has carried my system, router and DSL modem for 20 minutes on a power outage.
Hope this helps.