A.) This is from their
License Agreement:
If you have a valid Software license, you may set up an additional test forum in order to test code, template and database modifications. To make this clear to us and our license verification procedures, place it in a directory called 'testvb' and be sure to password protect it. It must not be accessible by the general public.
Mine is in a folder called 'test' and I have it available at test.mysite.org. This makes it easier for me to see exactly where I am at all times by hovering over any links.
Here's something from vb.com on htaccess. I htaccess protect my Admin CP, Mod CP, and my test site directory. I'm not sure if you have some sort of server software like cPanel or webmin, but I just use that to protect the directories. It then popsup a window like what you see when you go to the members area of vb.com - it asks for a username and password that you set up - not your vbulletin username and password. Since you must know the username and password in order to see the test site, it can't be crawled by spiders.
B.) If you go to your Admin Panel > Styles & Templates, one of the options is to Download or Upload the Styles. So, I download it from my test site and then after I upgrade my real site, I upload the style to my real site and it overwrites my old style with the new one which has all my newly modified templates.