VMware Fusion 2.0 Vista Optimization
Check out this great optimization article by the VMware Fusion team:
http://blogs.vmware.com/teamfusion/2008/09/optimizing-vist.html
They recommend these tweaks to get the most out of a VM with Vista running:
1) Disable System Restore
2) Disable Screen Savers
3) Optimize Power Management for Virtual Machine
4) Disable Windows Sidebar
5) Disable Remote Management
6) Run Windows Disk Defragmentation Utilities
7) OPTIONAL: Change to Classic UI
It all makes sense. System Restore isn’t required because of snapshots. Screen savers are unnecessary because the host OS (in this case, OS X) has a screen saver. The sidebar is totally ridiculous regardless of whether Vista is running in a sidebar or not. 
Check out the article for more information.