Think your current PC is good enough to run Vista? Well -- it probably is, if you don't want to take advantage of the new "Aero" GUI. Microsoft has stated that the bare minimum specs for running Vista (without Aero, that is) is an 800MHz processor, 512MB of RAM, 20GB of HDD space and a DirectX9 capable video card. That covers most of the PCs out there today...

...But if you want the new fancy-pants interface you'll need a DirectX9 compatible video card with 128MB of RAM or more (256MB of VRAM is required for "higher resolutions"; no specifics yet), 1GB of system RAM, a 40GB HDD, and a 1.0GHz or better processor. These systems are considered "premium-ready" and also require a DVD drive, sound output, and internet access to run the full-featured Vista.

Good old Microsoft keeps it in proportional: for every feature removed from Vista (and, to be fair, added features stolen from OS X), the system requirements go up.