Extend my iMac screen to my Old iMac screen | how?

Hi ppl,

I have a new 27" iMac and an old 24" iMac (Mid 2007)

I want to use the old iMac as an extended screen for the new one.

Tried to use AirServer with the new extend screen via AirPlay - but its leggy and I cant get it to work in the native iMac resolution...

Can't find a way to do it.. didn't the new Mavericks help to do it easier?