Received a 24" 2008 iMac (2GB RAM, 2.8 duo-core) hand-me-down that had potential, but was slow and had a smaller internal HDD. I'm unfamiliar with Mac's, but I also had an unused 120GB SSD laying around and figured I would tinker to learn Mac.
I decided to kill two birds with one stone and swap the main drive (startup disk), add the dual drive bay and upgrade tthe RAM for a major boost in performance. Note that although the Apple website says this iMac will max out with 4GB of RAM, it will accept 6GB. I found 6GB of DDR2 memory on eBay (one 4GB chip and one 2GB chip) for $89.
Overall, this was a very straightforward project and took me an hour, start to finish. I had the Phillips screwdriver, Torx T-8 and T-10, but had to order the T-6, Spudger, and suction cups wit the drive enclosure from iFixit. I laid out a towel on my kitchen table for a soft work surface and followed the directions on my iPad. Note: you should not install a drive in this enclosure that is bigger than 1TB. I think this has to do with either the OS not reading it or the nature of a PATA connection. Either way, follow the directions and you won't be disappointed. I installed a 1TB 2.5" HDD in place of the optical drive, and a 120GB SSD in place of the original start-up disc. (I found the 1TB hard drive on Amazon for $82 and it was cheaper to buy it in an external enclosure, than a bare drive). DOn't waste money on a 7,200 RPM drive for the internal, it is limited in speed by the PATA connection, but still faster than a typical USB 2.0
Before installing, I clean installed OSX 10.10 and all applications on the SSD. Note: you will need to double-stick tape the 2.5" SSD into the inside of the iMac case or customize a bracket for the SSD to fit in place of the standard 3.5" drive.
Once everything was buttoned up, I started the machine and formatted the 1TB storage drive, then aliased all of my storage folders (pictures, movies, music) to the storage drive. Check out this site for more info on that. http://mattgemmell.com/using-os-x-with-a...
Finally, I transferred my photos, documents, etc to the storage drive and it works.
These older iMac's are totally fine for regular PC use like: internet, office work, photo editing, etc.. Increasing the internal storage, updating the RAM and converting to an SSD added a few years to its life and makes it very fast to use. For the price, you won't regret it! One other benefit of this dual drive configuration is it free's up an external port and looks cleaner.