You only get on the Test Servers if invited by Disney, and no - you cannot request to be on the Test Servers via membership services or any other communication (you will get the standard reply of 'we are currently not recruiting new members for our test env')
If you are luckly enough to get a magical e-mail from Disney one day asking you to be on the Test System - you then D/L and install the program just as you would the Live Program - then after each play (or every couple of days) send them an e-mail with your Bugs / Findings.
