Shoutbox

What do you mean by "description"?

If you mean a different screen name or a different personal message, then no, this is not possible. Such information is stored per user, not per contact. This is the same for a display picture or anything else connected to your account, like your status.

Moreover, a contact can appear in different groups. So it wouldn't make much sense to have different stuff per group either (because what per-group setting would you use in those cases?).