Ha! I've done this before...but for HP-UX.
Basically the app at the time used a Perl daemon on a crontab to periodically issue a bunch of Unix commands, munge output, and send data back UDP in a lame '###' delimited protocol to a monitoring server. The monitoring server was also Perl, and each packet was then fed into a database as it was recieved and interpreted. A JSP+Applet system exposed the database tables to the web. Initially the monitoring service was also Java, but Java was slow and unwieldy for what we needed to do.
An easy project really, and it can be done well any number of ways. I'd definitely want some lightweight system doing this rather than using some evil enterprise management project.
Much easier and more fun in Unix though.
--Attila (who is not logged in...)