I recently read the thread helping out Alex: virtual-server/guest-vm-wont-boot-after-hyper-v-server-upgrade-t95528.html
and wanted to comment on a SIMPLE way to upgrade the Integration Components or Integration Services OR Virtual Machine Additions (what ever microsoft is calling them now) for Guest VM's being hosted on a Hyper-V box.
Although I agree with Mrgroove, you can just install a legacl VM adapter and use Windows Udpate to update to the latest. What I found is even easier is to:
1 - Upgrade Hyper-V Host with latest code - RTM, Hotfix etc...
2 - Launch the Hyper-V Manager MMC
3 - Connect to the Hyper-V Guest System (1 at a time)
4 - Click Action - Insert Integration Services Setup Disk
5 - Follow the prompts to install
The machine will reboot and finish up the installs but you should be golden at that point.
Let me know if you have problems or questions!