Thanks for your reply, given me a lot to think about!
Firstly, he mainly uses the computer for casual internet usage, with word processing for his work and very occasional photo editing (he's an amateur photographer).
Secondly, I believe it is the early 2008 model of the iMac, the one that started around April 2008.
I'm not so sure about upgrading the ram, it had 2 slots with DDR2 compatibility, so the max ram would also be 4GB, but it currently has 3GB anyway, not sure what difference 1GB would make. I'm not so sure he would be interested in anything like dual booting windows, he's definitely not what you would call tech savvy
Upgrading the SSD is actually a pretty good idea, I guess the main problem with that is that like I said he is an amateur photographer, so he stores a lot of photos, and is near the 250GB cap currently of the harddrive it came with. I'm not sure of anyway to fit a SSD and HDD like to can with PCs, one for the OS and one for all the photos would probably be perfect. I don't know if an external hard drive for the photos is a good idea?
Yeah you are probably right, I know mum loves her iPhone so she will probably appreciate having a better Mac instead of a better PC
Windows is probably a bad idea. I can see the appeal of iOS but I have been on windows for all my life so I think I was being a bit short sighted!