In order to make your IRC experience as nice as possible, we advise you hide the joins, parts and quits. When a room is over populated, and many people are coming and going, it can get very irritating to have your screen filled by these messages. In order to hide these messages, follow the instructions for your browser.
mIRC - Right click on the room tab -> Events. Choose either "Hide" or "Show"
XChat- Right click on Channel Tab / Tree Entry -> Untick Show/Hide Join Part Messages
XChat Aqua - Click on the options next to input box - Activate conference mode
Chatzilla - Please read the information at this link: 
Java Applet -