Using a lot of groups in my contacts list I had the idea to add an option :
auto expand contact group when some one is online (and close it when everybody is offline)

Is that possible ? What do you think about that ?

You can already group all your offline contacts in a separate group so that the groups you made get filled only by the online contacts assignet to them. When nobody is online, the group's empty. Is that maybe an answer to your request?

If you want to do KeyStorm's suggestion go to
Contacts(msn contact window) > sort contacts by > groups
the drop down menu will close, so follow those steps again
then select "Group offline contacts together"

I hope that;ll fill your needs

That's not what I'm looking for. let me explain a little bit...
I've already activated these options but when a group is open and no body is connected, there is a grayed message "Everyone in this group is offline".
Instead of showing this message, it should be nicer to close automaticaly the tree item of this group and reopen it automatically when a contact of this group is online.
Auto expand groups that have at least  one of they contacts online and reduce others tree items.

Have you understand whant I'm triying to explain ?