Cross-platform Volume For Libraries And Installed Applications

I am currently studying about file sharing and have recently developed an urge to create two volumes that can be shared across two Windows installations. One volume will be for the contents of the user files (My documents, My Music, Downloads, etc.) and the other would be for installed applications. The main reason I want to do this is because I am currently using a machine with a Windows 8 partition and a Windows 7 partition, and the whole process of having to copy the files and install the same programs to the other partition is really daunting, not to mention a huge increase in wasted space on the hard drive.The main issue I have with the first volume I want to create, is that I really have no idea how to integrate the user files in a way that both Windows installations can find it inside the same default location.All I could think of is maybe some kind of re-direct setting or file, but I still have no clue on how to do that. On the second partition, I have experimented with creating one similar to it for games only, but when I tried to run it on Windows 8, most of the programs needed to either reinstall, or have me manually add some dll files to the Windows 8 partition.