This is very common.

One way to do the auto-join of various networks without having it connect to the networks again from the Perform section is to use on START.

Code:
on *:start: {
  server irc.server1.net -j #chan,#chan,#chan
  server -m irc.server2.net -j #chan,#chan
  server -m irc.server3.net -j #chan
}


This will join all the networks/channels when you start mIRC and will only run when mIRC is started rather than Performs, which run whenever the server connects. There are other options as well. If you're looking for something different, please let us know.

Invision Support
#Invision on irc.irchighway.net