Just about to upgrade RAM - Which Slot?

I'm just about to upgrade my imac with an extra 2gb to add to the 1 gb I have already. Does it matter which way round they go? i.e. does the 2gb have to go in the slot that is currently being used by the 1gb ram?
I have the 2.0 ghz 20 inch alluminium imac that can have up to 4 gb RAM.
Any advice is welcome.

Nope no difference I believe.

You may want to open up system profiler and click memory, you may have 512MB in each slot adding to a total of 1GB so you would need to take one 512MB out to replace it with the 2GB for a total 2.5GB Ram otherwise it shouldn't make any difference which ram slot you use.

I don't even have a Mac yet (so may be wrong) but I was in the Apple store last week thinking of buying an iMac and the salesman told me that you have to have the same size memory in each of the two slots. So, I'd guess you have two 512's and if you wanted to go up to 4Mb, you'd have to throw them away and buy 2 x 2Mb. I'd be happy to be proved wrong by someone that's done it though

You dont have the have matched pairs in each slot, you only need to have matched pairs in each slot if you want to have the DDR2 Capability that both the computer and the ram use, so you can have a 2GB and a 1GB in each but you wont have the DDR2 running, but you would have the DDR2 running if you have 2x 512mb, 2x 1GB and 2x 2GB