Every two months it seems someone wants to take the iMac and use it as a monitor. I don't understand why. The thing is really not the greatest looker, weighs a lot and is bulky. It's also expensive as hell. Check the forums and you'll see maybe ten posts with the same question and the same answer: definitely not.
BTW, you are seem to be very confused... Macs do not run Linux and the iMac is not a display, it is a computer. If you want a stylish (overpriced) display than you can purchase the apple cinema display and run Windows XP on it all the live-long day.