The version 3 beta does not affect the installation of version 2, you are able to install and use these concurrently.
The only issue is that files worked on in version 3 cannot be opened in version 2.
Andrew is correct in that when you open a version 2 file in version 3 it does not overwrite the existing version 2 file (instead it saves a copy with a new file extension). However this means any work done on this file in version 3 cannot be opened in version 2. You can only open the original version 2 file.