Second, you can install both clients. Here is how to do it:
Go to your TSW account page
On the main TSW page, you'll see:
Download the Open beta, it will ask you to save "publicbeta-setup.exe"
Save the file called "publicbeta-setup.exe" in a specific new folder on your hard disk
Launch the file, answer the few first questions about language etc.
Then it will tell you that a TSW install already exist and will ask if you want to cancel the current install.
Answer "no" (I don't want to cancel this instal = I want to continue)
And then select CUSTOM install And then select a folder that is NOT the folder where you have the Closed beta client install Do not accept the creation of a shortcut on your desktop; you will add one manually if you want (in certain conditions it might overwrite your Closed beta shortcut: it's not a real issue, you can recreate it though)
Let the patcher download the game
Launch the Open Beta client from its own directory (or create another shortcut on your desktop of course)