Vista shouldnt be eating over 2GB of RAM. You must have had some stuff running on there. Even with 75 processes going at all times i still barely hit 1.5GB of RAM usage at any time in Vista.
Things like Outlook, Opera, µTorrent, Sidebar, F@H, Fahmon, WinAmp, Avast, WLM Beta and much more going at all times i have yet to break the 2GB of my 3GB in resource usage. Even when running things like Photoshop CS3 and much more i still never broke 2GB usage.