Ive tried many times myself and had other very capable webmasters that own VBulletin software try to install it for me, and it is just impossible to do it easily.
i own the software (its for sale cheap by the way) and just dont understand.
Without a cPanel username and error message, we aren't able to investigate this further. I'm not personally aware of any issues installing vB normally, but without any additional information there's not going to be anything we can do.
I performed the following steps to install vBulletin 4.2.2 and got it to work (although it was quite painful and time consuming).
Upload the "upload" directory to your public_html
In cPanel x3, go to the MySQL database wizard and create a new database and database user for vBulletin. Make sure to give the database user all privileges
Copy or move includes/config.php.new to includes/config.php
Edit that file and specify your database name, database user, and database user password that you generated in step 2. I've included the changes I've made below. In my example, I named the database "vb" and my user "vbuser". I'm also adding a table prefix of "vb_" so that I can install other things into the same database later on if desired
Browse to your site, the installer should appear and prompt you for your customer number. Enter it. Go through install process entering information as needed. For me, the installer froze at 92% on Processing XML Step 4 of 9. If your install freezes at some point OTHER than Processing XML, do NOT continue with the following steps and instead let me know what step it froze on (include both percentage and name).
Upload tools.php from the do_not_upload directory of the download into your install directory (so it would be located at /install/tools.php).
Browse to it, then click on each of the links in the top two sections "Import XML Files" and "Datastore Cache" (only do one link at a time). If any of those freezes or hangs (give it like a minute first), reload the page to make it continue from where it left off.
Delete the install directory. Your forum should be installed and ready to go!