Snow Leopard is an excellent OS and the last one capable of using Rosetta and will also empower you to use App Store. I have had an excellent relationship with it for 5 years.
I think your machine qualifies but the first thing to do is check out the formal specs needed for Snow Leopard.
If you pass that test ... you can go on to buy Snow Leopard 10.6.3 DVD.
In the USA go to http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard In Europe or elsewhere substitute your national code in place of /us above.
In the UK … the last known price was £14.
Before you start upgrading, back up your files.
Once you have upgraded to Snow Leopard you will need to apply the Combo updater. Mac OS X 10.6.8 Update Combo v1.1 and follow with a software update to pick up any later updates.
Your memory is sufficient at 2GB but 4GB would be better.
I would think you should be ok for 4GB but the recommended suppliers below will tell you. Many people on these forums speak well of them.
In North America contact OWC … Upgrade Apple iMac Memory
In Europe contact Crucial.com … RAM Memory Upgrade
Both companies have facilities on their site to guide you and will recommend the correct memory package to meet whatever needs you describe to them.
There may be benefits buying from your own geographical location insofar as Shipping charges, Local sales taxes and Exchange rates. Check out the basic memory costs and do your sums.
Thanks. According to them, I can upgrade to max 3 GB, (one 1 GB and one 2 GB module-thingy) so I may do that.
Is that something I can do myself or do I have to get it to a professional? I've read about tabs snapping off when incorrectly trying to open a Mac, or having to completely disassemble the entire machine to get to the part to be replaced, and exactly how to do it properly differs per model. The video Crucial has on their site shows a newer model than mine, so I can't go off those instructions.
I can't be sure how different yours is to mine in physical terms. With mine, a 2007 7.1 imac, 2.4GHz, Intel core 2 duo, there is a small plate in the bottom of the screen which can be removed. (Make sure you use the right screwdriver, the screws tend to mangle otherwise).
You can do it yourself. If you withdraw and insert the memory carefully it should be no problem. I am nothing special technically, but I have upgraded my memory twice so far without problems.
Both of the recommended suppliers will talk to you, one to one, on the phone and a number should be on their site. Good luck ... and thank you for the stars.