C:\MediaLab is the default path simply because it was first developed when Windows 95 was just a kid. To minimize the potential for path problems, we left it there because it played nicely with short file name conventions. Anyways, trivia aside, we are changing this in the new DirectRT and MediaLab betas to conform to the C:\Program Files tradition that has since evolved. As far as how you can have an influence in this, I believe you can simply change it during the installation when it asks you if you would like to change the path from its default.