If you just want to map windows versions to paths you can make a custom config section that would look like that: (I'm basing the version numbers on this answer)
<pathsByVersionSection>
<pathsByVersion>
<version major="5" minor="1" path="xp-path" />
<version major="6" minor="1" path="win7-path" />
</pathsByVersion>
</pathsByVersionSection>
and if windows 8 is added you will be able to add an element:
<version major="6" minor="2" path="win8-path" />
An example of making a custom config section with a collection can be found here