I think the Nagios network monitoring software (http://www.nagios.org/) has code that will check temperature via BIOS facilities. It is open source and works in *nix environments. You'd have to check it out though.
I know for certain that you can do this with the Servprise WebReboot Enterprise (http://www.servprise.com/enterprise.html). This device is Web services enabled, and you can get the temperature of any connected computer, although it's way overkill for a single computer.
As a disclaimer, I am affiliated with Servprise. I just wanted to alert you to the two options I am aware of.