Carl Tyler gave an interview on Collaboration Loop concerning rules of etiquette when using IM.  It is something that n00bies should definitely take a look at and even veterans would get some value from.

IM isn't email. Keep your messages focused and to the point. If it's going to take a few lines to send the message, think about whether email would be better. Use emoticons when required. IM messages can often come across with the wrong tone, so use emoticons (smiley faces) to indicate the tone of your message.