Based on my experience, I strongly recommend that you do NOT manually install WMDC. Instead, just connect your device to the PC via USB and let Windows 7 do it all for you. It will take a few minutes to download and install WMDC and the drivers, so be patient. This has worked perfectly on multiple Windows 7 machine I've installed and there is no reason it should not for you.
For those out there upgrading from Vista, make sure you remove WMDC prior to running the upgrade. You will be asked to uninstall WMDC anyway.
Do not hesitate to share your experience in the Comments area below.
Sent from my Windows® phone.