What will run faster, an iMac intel core2 2.0GHz with 2GB memory or the 2.4GHz with only 1GHz memory?

First, “faster” depends on largely on what you’re using it for: graphics, games, 3d, development, music—they all have different requirements.

As to which Mac to get, I almost always recommend getting the newest revision. Because of high resale value, in the end it’s usually the best option (e.g., you could sell the newest macbook for more 3 years from now). And you could through on the memory very cheaply (2 gigs is nice to have in os x).

Also, there’s no reason to ever buy memory from Apple… it’s weirdly expensive. Always get the minimum and then add it yourself. crucial is one of many companies that sells quality mac ram for pretty cheap—and it’s super easy to install yourself.

Ben, will installing new memory void your warranty?
I want to but a Mac too (as you may know) and 4gigs is €650,- more expensive!

Nope, it won’t void your warrarty. It’s one of the few installs they allow. I’ve even had Applecare work done on my machine with 3rd party RAM in it… no problems (though I would take it out before you ever take it in for warranty work, because they don’t want to be hassled to fix things that they didn’t make).

But it’s totally A-Okay. So, definitely, definitely, get your RAM elsewhere.

My advice is always to buy the fastest processor and most RAM you can afford. That $150 may seem like a lot to you today, but when you think of the time you spend over the life of the computer waiting for the slower one to get things done, you’ll be happy you spent the extra money. BTW, I recently bought 4 gigs of RAM for under $200 from macsales.com.