Big Brother System and Network Monitor, will probably do most of what you want. It is extensible and plug-ins can be written in any language. They have a free editon of their monitoring software:
http://www.bb4.org/home1.html
You should also use a local monitor on each server that is being monitored. This is because it is difficult to diagnose problems remotely. This blog has a good discussion of the problem and details of a local monitor design pattern:
http://sleeksoft.co.uk/public/techblog/articles/20041218_1.html
