Your license allows you to set up a test site. Just make sure it is .htaccess protected so it isn't open to the public.
As Brandon said, shut down your live site to make the backup. What he didn't say is that after you shut it down, change the Forum URL to the test site URL and set the Cookie Domain and Cookie Path to default (nothing) and then make the backup you will use for your test site. Then change those back and open up the live site. That will save you having to change those things in the database especially since it is save as serialized data in the datastore table (and most people don't know how to deal with serialized data).
Also, if you put your vb5 files in a /directory, you will need to change this line in your .htaccess file:
#RewriteBase /
to this line:
RewriteBase /directory/
|