In addition to what Andre says, if you are looking for minimizing guest RAM requirements, you might want to turn off 3D acceleration. Of course it depends on your need if you can do that.
The following link explains what it uses: Hardware specifications it's a link from VMware Fusion 4.x so might be slightly off in factual numbers, but it gives you a good idea and I suspect that the numbers are still pretty accurate.
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Wil