How to find out who remotely logged into my Macbook?

I'm using a late 2008 version Macbook with OSX 10.6.8 and I recently discovered that someone has remotely logged into my mac and quit applications, opened Finder windows, etc., through their Terminal. I know its someone on my wireless network, someone I know, just doing it as a joke, but is there a way to find who exactly is doing it so I can get them back?

Thanks!