This probably means that you need to upgrade to RC0 Integration Services for Hyper-V. This is KB949219 which is publicly available from the Microsoft download center. This needs to applied inside Win2k8 VMs, since integration services shipped with the core operating system and they need to be upgraded. Since Win2k8 shipped with integration services, you are gettting the error that "integration services are already installed" when you try to deploy them from VMConnect.exe.
This is the same upgrade package that you can use to upgrade your Hyper-V Win2k8 server. The same update can be used for patching your Win2k8 guest virtual machines, but you have to patch them from inside the VM.
You can update these in a couple of ways:
-You can attach a legacy network adapter to the VM and go to Microsoft download center and download + install the update
-you can download the update and "bake" it into an ISO and attach the ISO to the VM. FYI, the same process applies to both 32bit and 64bit Virtual Machines.
A note of caution:
-Since Hyper-V initially thinks you have the integration services but they are not the right version, when you are trying to connect to a VM over RDP, your mouse might be captured. Ctrl-Alt-Left will not work in this case in terms of releasing the mouse. Instead, press Ctrl-Alt-End to release it.