Now I'm rocking an older dual-booted Imac with the stand cut off and mounted in the v-berth, so that I may blow my enemies into tiny bits (TF2 ftw) or curl up with Hulu while at the dock or via inverter in a pinch. I also picked up a netbook to do my casual work and surfing from the salon table, or to act as my chart plotter when I hook it up to the GPS. It works for me, but you may have grander ambitions. Good luck either way and let us know if you devise the perfect setup.
Dude - the iMac thing is kind of brilliant, I must say. Sweet.