Windows freeze is almost certainly driver related, ensure you have the latest drivers for absolutely everything - check the motherboard bios (be careful if you flash it), chipset drivers, graphics and sound card drivers, any extra cards such as a SATA controller card, network drivers, mouse, monitor (if required).
My freezing issue turned out to be an out of date motherboard bios (meaning the hard-drive controllers were out of date) but this has not been the case for everyone.
Edit: Make sure you get the drivers relevant to your Win7 version, i.e. 32bit or 64bit. If no Win7 drivers are available, try Vista drivers.