The responsibility to get the iSight working with that software lies with the developers of that software, and as they currently have not implemented that, you may be out of luck.
Have web searches brought you any results ("isight with msn/yahoo messenger")? Have a look at adium, it supports several chat protocols, but I don't know about iSight support.
A more descriptive thread title would also help attracting more knowledgeable persons concerning that matter though.
Your title is to far spread. I just clicked on it, because I was expecting issues with a video camera or something in that vicinity.