Joao,
Yeah that would be nice, but irc, netmeeting do not use the proxy as they use certain ports, to block them I had made a list of known ports, like 6667 6666 for irc and others for IM programs and P2P programs and just used a port blocking rpm to close them, I know users can then change the port that the certain program uses but that would be only a minority of users and thus discourages the average user from using such programs.
That is the only solution I could think of and it has worked, aslo I get called around a lot to users computers and then I do a manual check of installed programs, but this is not a problem on windows 2000 machines as I just set the domain policy to dis-allow the installation of programs.
There is probably a better way of tackling this problem, I am just suggesting what worked for me, good luck!
Cyrus Bharda