You will have network naming collisions and possibly other problems if you completely synchronize the physical machine's OS partition and the VM's OS partition, and both are running simultaneously. There might also be licensing issues with synchronizing the two Windows installations, if you don't have a volume license.
If you just want to synchronize data, that's easy. On my workstation, I just share the host's data partition as a Windows network share, then map that share to a drive letter in the guest OS (Click the "Tools" menu in Windows Explorer, then select "Map Network Drive..."). I use the same drive letter on both the host OS and guest OS. No syncing necessary. ;) Of course, this won't work if you're only running one of the two machines (physical or virtual) at any given time.
If you don't run both machines simultaneously, you can use DropBox to synchronize a specific folder on both machines automatically.