I was thinking about using my old iMac as an addition display with my new iMac. I found some info on this in a article about Macs. There is an option called ScreenRecycler. Software made so you can use your old Mac monitor, Powerbook, or even Windows PC. I decided against this since my office is so small. I prefer more desk real estate. Less clutter. But the ScreenRecycler is an option if you really don't want to part with the old.