I've not tried with any modern devices but the older UPS's used to toggle the CTS or DTR data line on the serial-port to tell the PC that power was available.
The driver would simply watch the pin and when it toggled the software would start taking action. These lines are still made available via the USB driver but it looks like the issue is with the installation section. -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
