the ram available with vista simple or vista with sp1 is not relevant, because the windows will set a value that dependents from one hardware configuration to another hardware configuration.
Also in time the windows try to optimize the space that he (vista) use in memory. So if you have a pc with a clean install and one pc with vista installed two weeks ago, the vista space in memory will be different from one pc to another, even are same configuration.
that was all with vista memory eating
and now ... my vista say the sp1 patch on the windows update list (that from vista) will need 120MB space to download..
I also wait
to see if will have a positive impact on the masses