First, I want to say we are really glad that you are interested in the new version of Sitefinity and that you are willing to give it a shot.
You should not have any problems running 2 versions of Sitefinity on the same development machine. Sitefinity by default is installed in a different folder to the old versions and it creates a different virtual directory which leaves your old installation in tact.
Let us know how it goes!
the Telerik team