Can I install Mavericks side by side with an existing installation?
Yes, you can install OSX onto any eligible partition or external drive and are not constrained to simply apply it on the running OS. 

Download the installer and choose any destination when it prompts you to install over the running OS. 

I prefer this in almost all instances since I can run the migration to my new OS without ever losing my current setup or wiping a system that is currently in use. It only costs disk space and one extra step when installing.