vbulletin is a template-based system - you can edit the templates to suit your needs
Skinning: Understanding A Template-Based System
http://www.vbulletin.com/docs/html/styles_and_templates
if you know nothing about XHTML/CSS; editing of templates etc - you should hire someone
WARNING: your topnavbar CSS may conflict with the vbulletin CSS - some editing may be required