Most Longhorn builds have an expiration date. To make them work, you must change your VM's to 2003 or 2004
If you're looking to simulate or experience Windows Longhorn (Vista) for work or nostalgic reasons: windows longhorn simulator work
Some enthusiasts run up to 12 different Longhorn builds simultaneously (Build 3683 to Build 5048) on a single physical machine using nested virtualization (VMware inside Proxmox). This allows side-by-side UI comparisons and regression testing. A dedicated "Windows Longhorn simulator work" rig might feature: Most Longhorn builds have an expiration date