Coherence, drag n' drop among other services are enabled via the correct installation and working of Parallels Tools (drivers, services), unless there's something conflicting with it and its installation, re install should take care of the issues. If the problem persists something might conflicting with installation.
AFAIK, in the latest versions of PDM7 and 8 Parallels Tools works as expected with Windows XP up to Windows 8, leading to conclude there's something peculiar in your setups.
My suggestion, contact Parallels Support.
Last edited: Nov 17, 2012