I had a friend (don't know where he is anymore) that I let get into my Mac from his house to he could help me. He had a Mac, too. Isn't something screen sharing or something?
I was looking at the App Store while you were posting, and ScreenSharingMenulet ($1.99) and Easy Remote Desktop ($0.99)
sound like they'll work. (There's always AppleRemoteDesktop, but it's $79.99.)
And yeah, you're right, there's /Apps/System Prefs > Sharing > Screen Sharing, but I don't know if it works for what you want to do.