I run Vista Ultimate, on 2GB RAM and Core 2 Duo, I have no problems with running multiple applications. My memory usage never goes above 56% on normal use(which is generally a lot of apps open - including Photoshop CS3 an Dreamweaver.)
People need to realise that their systems are old, you want to run new exciting things, you need new(er) hardware. I don't understand why everyone has a problem with this, sure it costs you money, but no pain no gain.
EDIT:
quote:
It'll better to have some automatic turn off mechanism when you run something that doesn't need it.
There is. All Aero features etc are turned off when you run a full screen application.