I suggest that a code be written for a popup or a buzz sounds comes alive when someone who you need to conversation with comes online. There should be urgent ways to contact the ppl you need to talk with as soon as they come online. Especially when they have many private emails and it takes days for them to completed them all.
I think IM are great but you can also become invisible. Not everybody has an IM so that why this would be a great assess you this forum. IM are for your desk top communication noway you can do that on this forum.
It would place a big strain on the site when the desktop solution really is your best bet. It is, as someone mentioned before, re-inventing the wheel.