Wanted dual hard drive for our aging iMac 24", so glad that iFixit has the PATA drive enclosure.
Overall, took 2 hrs to finish, open to close. I took my time and was tired at the end of the work week (a Fri night) -- wanted to be able to work on the clean install of Mavericks over the w/e. Had a vacuum handy to pull out dust in the nooks and crannies as I went. I took the advice of other posters here, and did not detach the lcd power cable (pic attached). I simply rotated the display out of the way -- definitely the way to go!
I used the iFixit guide app on my iPad as I went - everything went as advertised -- thanks guys!!
So, have clean install of OSX on 120GB SSD in main bay (OWC transplant from my MBP); plus 750GB HDD (Seagate Momentus XT 750 GB 7200RPM - another MBP transplant) in the drive enclosure. Keeping our rather large iTunes and iPhoto libraries on the HDD. System works nice and fast now, sweet. Will be using this iMac as backup system to MBP and will be used as media server via Apple TV.
If you're on the fence about doing this, my advice is to go ahead and just do it. I no longer feel the urge to buy new iMac. Loving the fact that this circa 2008 Mac is purring along into 2014 with the latest software, and essentially lag-free.