Okay your site is here
http://www.blahblah.com/threads make a new database for the test site
install a fresh threads to a new directory say
http://www.blahblah.com/test and complete the install and play. make sure the test one points to the new database. You can even import a backup of users posts in the new forum. If you do this do not run the createtables on the treads install. At this point you would upload your backup and then Make sure to run all altertables on the database.