Further to my post I would add that you should get a machine with the most amount of memory that you can afford 8gb or 12gb is not uncommon plus you need a 64 bit operating system of course. 

My previous comments were for clarification that even though offrench had OOM errors with 4GB with Vista(even though only just over 3GB is addressable) I infact have not had those errors so don't be put off in getting less ram if its not in your budget :) 

Ram is cheap enough these days to get yourself a lot of ram for little money.

Jon

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