My strongest recommendation to anyone wanting to experiment with hacks / templates is to create a mirror of your boards - that way if it breaks you haven't caused the users of the board any grief.
The most painless way to do this is as follows:
1) Start by downloading XAMPP
http://www.apachefriends.org/en/xampp.html
2) Install it on your local computer. The XAMPP pages provide thorough instructions for this.
3)Once it's up set a password to your xampp pages this way outside users can't see your mirror boards. Go to
http://localhost/security/xamppsecurity.php to do this (if that url doesn't work xampp isn't running on your computer).
4) Copy all your /forums directory to the /htdocs directory of your xampp installation.
5) Close your forums
6) Log in on your server and type
cd ~
hit enter then type
mysqlhotcopy --user=root --password=YourPasswordGoesHere databaseName ./
7) Open your forums back up
8) Download the directory created by this to your local machine.
Depending on your forum size this could take awhile. If the forum is large consider creating a zip file first.
9) Copy the forum over to the /mysql/data directory of my xampp installation. Make sure that you only copy the directory containing the files of your database - there will be 3 files per table in your db all contained in one directory. That containing directory is what you copy to the /data directory of mysql. Don't MOVE files - COPY them - if you mess your mirror up while experimenting you'll simply repeat this move to restore the mirror.
10) Go to http://localhost/phpmyadmin and create the user name and password your forums use to access the database - this will be in the forums config.php file. Just go ahead and give this user global priveledges - you don't need to fine tune it on the test board (though if you know how it doesn't hurt).
11) Go to http://localhost/forums and you should be able to log in. If you run into cookie problems you may need to move tools.php from the do_not_upload directory of your forums' install package into the admincp directory of the mirror.
And that's the basics of mirror creation. It's tricky, but it's worth the effort.