Yesterday I took apart my mother's iMac to put in a new hard drive and memory and install Snow Leopard, the current Apple OS for the Mac.  Her system had been running two versions behind and was exhibiting strange behavior.  The iMac was difficult to open and, contrary to the way most iMacs were built until the aluminum models came out, this one opened from the front.  I couldn't find help on the 'Net, but figured out how to remove the LCD panel (built in screen) so I could get to the hard drive underneath.