UPDATE: so the imminent snow leopard came and my iMac failed the upgrade-install causing the computer to flash ?-folder icon. this started another day-1/2 lost doing the perpetual install-dance of installing os x tiger to the iMac. installation would cause error in the middle of it and sometimes it would come through all the way up to the welcome video and once past the welcome video up to the desktop. but, inevitably, the iMac would keep freezing. i spent an entire day doing this dance because i didn't know what was wrong. at first i thought it was a finicky iMac superdrive, so, i used my mbp in target disk mode to install tiger to no avail. disk utility shows the iMac's hard drive and after erasing it--it would pass all verifications. sometimes, disc utility would show iMac's hdd as "media" and googling it showed results of this as a sign of a dying hard drive. this made me realize that the iMac's hdd is also dying. and the reason that the iMac let me install tiger and even install all the updates the first time was because i did a 7-pass erase the previous night. i didn't wanna do this again just to work for a bit and then die. so, i came to the conclusion that even though disc utility repaired my hdd and verified it after erasing prior failed installations--the iMac's hdd was indeed going under. it is corrupt or full of bad sectors and the 7-pass erase only delayed the inevitable. my only solution then was to sleep the night off and then buy a new hdd the following day.
the next day, i grabbed a new hdd from the nearest store. i also realized that this would mean that i would have to open up the iMac myself. thankfully, the ifixit guide showed me that this would not be so bad. and, it wasn't. opening up the iMac is straightforward. lots of screws and some untaping and unplugging of connectors but straightforward and fairly easy. this is on a mid-2007 iMac by the way that is out of warranty so this was my only solution if i wanted to save money. it's even possible not to unplug the lcd temp from the lcd panel itself and one could work on the hdd with the lcd panel still attached but has enough give to let it be out of the way, safely. so, i took out the old hdd and put in a new one and this was also straightforward and easy. so, after this i put back the iMac and held my breath. then turned on the iMac. i didn't hear the chime sound but could hear the dvd spinning as i inserted the install disc. the iMac's screen was still blank. "uh-oh," i thought. and then i realized that i might not have put the inverter cables correctly. there are four of them and i might not have put them back in the correct order. so, i had to open up the iMac again to switch the inverter connectors. I switched the first two connectors then turned on the iMac without putting everything back in just to see if it worked. luckily, it did. so, for future reference when opening up a mid-2007 20" iMac, the four inverter cables underneath the lcd panel can get easily mixed if you don't label which connector goes which way. i then decided to let the iMac run and install tiger with the guts still showing before putting everything back on. then, tiger did install and i breathed a sigh of relief. i put everything back on the iMac and is now doing ok--having been upgraded to snow leopard even.
so, the problem with the iMac wasn't a finicky superdrive. in fact, the superdrive is fine, although a bit loud. the problem was a dying hard drive. a corrupted hard drive. whatever you call it. it needed a new hdd. i just wished i had known it earlier because a dying hard drive is not so obvious. just thought i'd report back here.
