Currently there is no free and easy way to directly export a Quicktime with Apple ProRes on a Windows PC. Fortunately Avid offer their DNxHD Quicktime codec and others for free: http://avid.force.com/pkb/articles/en_US/Compatibility/en263545
DNxHD provides the same quality as Apple's ProRes. Just unzip and install the codecs. Now they are available in the Quicktime export / render settings of your favorite editing and compositing package. Choose your image size and bitrate in the codec settings according to your needs. You may want to try a couple of settings to get a feel for the quality of the outcome. I have also been getting nice results with the Avid 1:1x codec as an intermediate export to another video encoding software such as Handbrake. But beware of big file sizes with the 1:1x codec!