i found a simple and good IRC client for your Milestone.
Its aviable via Marketplace and called "DaraIRC".
 Download DaraIRC via Marketplace
 Start DaraIRC
 Hit Menu button
 Choose "Add Server"
 Enter Server specs: irc.yourserver.com
port stays normally
 Add a channel
Only one thing should be noticed, this client sometimes has problem when a message is entered via the Touchscreen, so use the keyboard instead. This has also the effect that you lern fast typing on it