Actually, you can install two different versions of DS4 as long as you use separate accounts on your machine to do so. However, the CMS is a shared database so you will need to make your content directories shared folders (not in the Documents folder, ideally, though that can be made to work) in order to use metadata and categories. However, as prixat says the application is the same (as far as the 32 bit version goes), it's just a question of which plugins are enabled.