Thanks to you both (also to a fellow Australian?) but I am far away in France; hang with me please I am not totally computer savvy, however I have found out this info
2.4 GHZ Intel Core Duo
Mem 1Go 800 mhz DDR2 (or Z?) SDRAM, can't sem to find available memory will ask my son!
Had a new hard drive fitted about 18 months ago,( Hitachi the boy said it was large capacity one)? as the previous one kind of gave up, otherwise the I Mac is fine, and I don't like much Firefox; maybe because I aint used to it? lol
According to Everymac.com, the 2008 iMacs are in fact capable of running Yosemite. However, we'd need to know more about your hardware to determine if it'd be a good experience for you. I'd settle for no less than 4 GB of RAM to run anything newer than what you have now. You can install up to 6 GB of RAM in the 2008 iMacs, so if you need more RAM, you may as well max it out. I don't know which exact 2008 iMac you have, but here's the specs page for the 20" 2008 iMac: iMac "Core 2 Duo" 2.66 20-Inch (Early 2008) Specs (Early 2008, MB324LL/A, iMac8,1, A1224, 2210) @ EveryMac.com
I'm typing this right now on a late 2008 macbook unibody with Yosemite and all that goes with it. Installed are 8G's of ram and an OWC SSD. Its like a brand new machine that I just purchased. No wait time on anything.
Thanks guys, you are a great bunch I hope I haven't burdened you all too much; my son is now going too sort it all out after all the info you have provided.
I am currently suffering from slow internet connection Youtube playback at only 140p apparently caused by by our IP SFR, I thought it was my Mac, but it turned out not be the case, so I can keep it a bit longer of course with the agreement of Mr Google? lol