Can buy both in the UK and in the USA as I travel there for business quite a bit. How much am I looking to spend? can you recommend good places to buy?
Few things first...I'm assuming you mean 4GB not 4MB.
You are going to have to replace the RAM in the computer. You can't just add to it. They put in 2 1GB sticks, so, you have to replace them with 2 2GB sticks. As far as where to buy, I want to know also. Prices are a lot lower than if you buy from Apple, that's for sure.