blocking irc + botnets

[hbeaumont hbeaumont]

Can anyone help me with the proper method to block outgoing requests to 
botnets + irc?

Or point me in the direction of searchable list archives (I could only find 
the non-searchable archives) or other FAQ that answers this?

Problem:

We have servers that could get infected via poorly wrote user scripts. I 
want to prevent these servers from being used as part of botnets or general 
connections to 
IRC (most scripts I run across seem to try to connect to IRC). I want to 
take the best preventative measures I can in case one of the machines would 
become infected
or otherwise compromised.

Also, interested in any other popular method of stopping general outgoing 
DOS attacks (rate limiting UDP perhaps? I'm not real up on the techniques 
used by the DOS'ers).

I'm interested in the recommended rules to add to prevent this type of thing 
should it occur. Thanks.