Here is the procedure that should get you the best results:
1) Download the drivers via the link above, but do not do anything with it yet.
2) Download and install a program called
Driver Fusion.
3) Uninstall your present video drivers by going into control panel, Programs and Features, and selecting AMD Catalyst from the list. Choose the option to Express uninstall all AMD software. Let the program do its thing. You will have to let it remove the drivers as well as the Catalyst install manager itself.
4) Reboot your machine when it asks, but do so in Safe Mode. To do this, hold the alt/option key on your Mac to bring up the boot menu. Select your Windows partition. When the screen goes black and you see a cursor flashing in the upper left corner of the screen, press the F8 key. This will bring up the boot menu. Select Safe Mode, and your machine will boot. As a side note, I would highly recommend having a USB mouse connected to your MBP, as sometimes the Trackpad will not work correctly in Safe Mode.
5) Once the machine has booted, run Driver Fusion via the start menu or desktop shortcut. Select "Display" from the list it gives you, then AMD. The program will scan for leftover driver files. You can delete them all. The free version of Driver Fusion does not allow for removal of old registry entries, but that's OK. Once you've removed the old files, the program should ask if you want to reboot. Do so normally (eg not Safe Mode).
6) When you're back in Windows, you can run the installation program for the file you downloaded in Step 1. Let it run, and you might have to click a couple extra times because they are a beta set and haven't been fully signed off by Microsoft. Reboot one last time, and you're done.