If virtual machine bus is disabled, follow this procedure:
Did this vm originally come from Virtual Server or Virtual PC? Or did you create it from scratch in Hyper-V?
When a Vista or 2008 vm comes from VS or VPC, you need to:
1. run msconfig
2. go to the Boot tab
3. click the Advanced options button
4. check Detect HAL
5. click OK
6. click OK
7. reboot the vm
8. apply Integration Services
(from John Paul Cook)
