I keep getting asked this question so here is the guide to AIM URL’s
You can use AIM (AOL Instant Messenger) codes in hyperlinks to interact with the AIM or iChat clients. Here is the list of AIM codes and how to use them:
To use a space
If you want to use a space be sure to place the ‘+’ symbol where there would normally be a space. aim:goim?screenname=SCREENNAMEk&message=Hello,+this+is+a+test!
Example: Click Here (You know you want to)
Opens a new blank IM window
aim:goim
Example: Click Here
Opens a new IM window with a screen name
aim:goim?screenname=SCREENNAME
Example: Click Here (You know you want to)
Opens a new IM window with a screen name and a message
aim:goim?screenname=SCREENNAME&message=MESSAGE
Example: Click Here (You know you want to)
Opens a chat room
aim:gochat?roomname=ROOMNAME
Example: Click Here (You know you want to)
Opens the "Add Buddy" window with a screen
name to add
aim:addbuddy?screenname=SCREENNAME
Example: Click Here (You know you want to)
Opens the "Add Buddy" window with a screen
and a group name to add
aim:addbuddy?screenname=SCREENNAME&groupname=GROUPNAME
Example: Click Here (You know you want to)
To change someone’s buddy icon when they click on the
link
aim:buddyicon?src=BUDDYICONURL
Example: 
To open or receive someone’s
shared files
aim:getfile?screenname=SCREENNAME
Example: Click Here (You know you want to)
