That would be against the license agreement. Specifically this:
Quote:
vBulletin licence grants you the right to run one instance (a single installation) of the Software on one web server and one web site for each licence purchased. Each licence may power one instance of the Software on one domain. For each installed instance of the Software, a separate licence is required. Modifications to the software or database to circumvent the one-license-one-board rule are prohibited.