Using phpSysInfo it is quite easy to set up a simple monitoring on any web server that runs PHP. Also, this script can display temperatures and fan speeds (via lm_sensors) if you configure it to do so.
It runs on most platforms and installation is very easy - just decompress and untar the source into your webserver's document root.
Here is a quote from project page:
phpSysInfo is a PHP script that displays information about the host being accessed.
It will displays things like Uptime, CPU, Memory, SCSI, IDE, PCI, Ethernet, Floppy, and Video Information