I've also heard about the 40G partition mentioned elsewhere as good for vista. I am installing on a 250G system and was thinking about a 40G partition purely for the op system. Leaving only 200G for everything else I want to do, which does not make me happy.
In one of my other posts a couple of people have mentioned 80G partition as necessary for vista. I was thinking maybe they have a point because Vista is famous for devouring resources and being huge. I understand 7 is just as big.
So I figure it this way: to be safe, 80 X 2 is 160G partition devoted to 2 op systems, and I'd hate to use half a disk just for the op system, the op is just a utility to enable the programs you really want to run. On a 300G disk the ops would take half the space! So I'm thinking 400G
I'm thinking about revising my vista partition to 50G (sigh).