Under which language is vbulletin created?

[James Birkett]

Yeah, vBulletin is programmed in mainly PHP, using MySQL whenever any database connection is made.
It also uses some JavaScript/AJAX functionality, however not a major amount.

All of the above can be learnt at w3schools. A simple Google search will retrieve plenty of tutorials.

As Lynne said, you can modify the style by editing the CSS (or templates) in the Styles & Templates manager.

Refer to the vBulletin User Manual for help.