Martin, Please check this link: http://www.microsoft.com/technet/windowsvista/evaluate/hardware/vistahardware.mspx
From Microsoft's own site, as for hardware guidelines, "just about any mid-range and better processor...you should have at least 512 MB of RAM" and "pay special attention to making decisions that give you maximum flexibility later to upgrade individual components"
I own a first gen Mac mini and it runs Grageband 3 wonderfully even while I have a browser and iTunes open concurrently.
And all the iLife apps are included with any new Mac purchase (including Grageband.)
Microsoft Vista: Another Reason to Switch to Apple