When I visit the Settings page I get the following error:

warning: mkdir(files): Permission denied in /.../includes/file.inc on line 91.
The directory files does not exist. 

Drupal uses a single directory for the storage of various files (for example attachments to content). When you visit the settings page it will check if the file directory exists and tries to create it when it doesn't exist.

However if the webserver doesn't have write permission (and it shouldn't) in the directory where the file directory will be created you'll get an error. In order to fix this first think about the name of the directory you want to use. By default Drupal uses the name "files".

Depending on your site layout you might need to change the cookies settings within vBulletin. This page will guide you to the settings you'll have to make.

The following Drupal modules work with vbDrupal but have not been fully tested.

EventFinder
Filemanager
Print Friendly Pages
TinyMCE WYSIWYG Editor
Workspace
Tax

The following Drupal modules work with vbDrupal with issues

E-Publish (sql errors upon trying to delete a section)
Event (date/time bug under headings)
location (API, module) (breaks other modules)

The following Drupal modules do not work with vbDrupal:

Comic
Project
Checkout (sort of works, but generates errors on seemingly-random occasons)
Contact Directory
Delicious
E-Commerce (5% tested, good so far, but probably will not work at payment stage or for auctions, according to Tamarian)

The following Drupal modules are confirmed to work with vbDrupal:

Amazon tools
Poormanscron
Excerpt
BBCode
Article
Bookmarks
Book Review
Control Panel
Excerpt
Flexinode
Forms
Htmlarea
Image
Img_assist
Movie Review
Poormanscron
Simple Access
Smarty theme engine
Taxonomy Hide
Taxonomy Menu
Theme Editor
vBlocks
Webform

Installation:

1.  Download the latest version of vbDrupal.

2. Edit the file forum/drupal/sites/default/config.php_new and enter your drupal and forum directory path. Save as config.php, then upload the full drupal directory as is (in full) to a directory of your choosing on your server. You may rename the drupal directory to something else if you want.

3. Import the product-drupal.xml file through your product/plugin menu. The steps, in case you have not used the product manager before, are: go to your AdmincCp -> Plugin Systems -> Product Manager -> Manage Products. Clcik on Add/Import Products links, click the "Browse" button, locate the product-drupal.xml file on your local PC drive, select it, and click "yes" to the "Allow Overwrite" option, and click "Import".