Login to cPanel and look for "Password Protect Directories"
Click that then navigate to the testvb folder (probably click the little yellow folder next to www first, then testvb)
click the "Password protect this directory:" box
Enter "test vBulletin site" for the name
Enter a username/password
browse to
http://waltdisneyboards.com/testvb and see if you are prompted for a PW (you may need to switch browsers, or close your current browser then try due to caching)