Finding the usergroup of the last poster?

[Cryo]

For my forums I want to give the last poster of a thread a different color username and potentially a small graphic to indicate they are "someone special" (ie. a developer for a game). I know where I need to CHANGE the code, but how do a I figure out the usergroup of the last poster?

For example...

Thread Name -------------------- Last Post by (Username) ----- Replies -- Views

Thread Name -------------------- Last Post by (Username) ** ----- Replies -- Views

Hope that makes sense.