You can put 2 256mb so-dimms in the tray load iMacs. You can install any size ATA (not SATA) you want, but the computer will only be able to use 128 gigs. Also, if you use a HD over 128 gigs you may not be able to access the data on the drive if you put it in a newer mac. Whatever size drive you use, you need to make a partition smaller than 8 gigs at the beginning of the drive to install OS X in. The newest version of OS X you can run is 10.3.x. You should be able to install a laptop style DVD drive, but I'm not sure how much luck you are going to have with the faceplate. I'm also not sure if you would actually be able to watch a DVD, as I'm not sure that old of an iMac has the horsepower to pull it off. It's a bit borderline. If you don't mind how it looks, you could use a slot loading drive from a later PowerBook or iBook.