Yes, you can install multiple versions of RapidMiner in parallel. Simply download the ZIP file version of RapidMiner and install/unzip it in any directory you like. For details about the installation from a ZIP file:
http://rapid-i.com/content/view/17/40/Of course installation through the automated windows installer is much easier, but through the ZIP files, you can install as many versions in parallel as you like.
Best regards,
Ralf