Example HTML : Replace SCREENAME with your AIM name and add the URL of the IN.jpg and NOTIN.jpg with the URL you host your in and out images.

<a href="aim:goim?screenname=SCREENNAME"><img src="http://big.oscar.aol.com/SCREENNAME?on_url=IN.jpg&off_url=NOTIN.jpg"></a>

The HTML source in use from http://www.macminicolo.net/contact.html

<a href="aim:goim?screenname=jaymenna78734"><img src="http://big.oscar.aol.com/jaymenna78734?on_url=http://macmini.purestatic.com/i_mini/saleshere.jpg&off_url=http://macmini.purestatic.com/i_mini/salesnothere.jpg"></a>

Here is the live results in our case (notice the slight delay as it talks to AOL?)

As far as I can tell there is no way to force it to open up a video or audio chat. If I am wrong please ichat me!