It all depends on how you use it, what programs are run, how much you keep running in the background, and how much free ram is available. More never hurts.

RAM is the memory a computer temporarily uses to run programs (in basic terms). If you buy a Mac computer then 1Gb or RAM is sufficient for casual users. The kind of people who use computers for the internet, word processing, pictures etc. If you tend to use programs that are demanding- 3D games, advanced video editing etc it may be worth making it 2Gb. You can do this on the apple store, it is difficult to do afterwards. I am very jealous if you are buying an iMac, I wish I had one- I yearn for a computer that actually works! EDIT: Well I have never produced music myself, so I can't really help in that department. I've found when buying other apple products that the staff in their dedicated stores are actually knowledgeable, so it might be worth asking them. I will say that it can't hurt to go for 2Gb, even if it a little more than is needed the computer would be useful longer into the future, so may save money in the long run. If you do buy a PC then I would definitely go for 2Gb if it comes with vista. I have vista and apart from the way it looks (which is quite nice) I've noticed little difference to XP, but I have 1Gb RAM and it gets used up quite quickly with just a few programs open. Some of my friends have Macs, and if I could afford one I would get one in a flash (you can even run windows side by side with Mac OS)- Macs just seem to work and I'm tired of fighting with windows!!!