While Vista probably won't be out until after the holidays—barring, you know, any further unforeseen technical difficulties like, say, the entire thing being as secure as an open box of cobras—you'll need at least 512MB of RAM (Read "2GB") and a DirectX 9 graphics processor (Read "a Cray") to just boot up. Want all those beautiful widgets and sexy transparent windows? Get thee a high end graphics card.

Vista Guidelines [Microsoft]

Program to label PCs "Vista ready" [Seattle Times via TheInquirer