ass long as the sites created with V1 are PHP sites you will still be able to edit them in version 2 with out dificulty.
Version 2 is only PHP compatible, if you have sites that are created in aother languages you will need to use V1 to maintain them.
If this is the case, you would need to create a new user on your computer, under this second user, you can install V1, and have V2 installed for the main user.
When you need to use V!, login to the second user account, for V2 log into the main user account.