How to visit companies and start-ups in the bay area?

Hi!

I am in the bay area hosted by Oracle, as the winner of the Thinkquest Digital media competition. I have two more days left here and I would really like to visit the big companies in the area(the offices, not just the campus) and other smaller start-ups. I am studying engineering at the University of Manchester so I am really interested in this field.

I was wondering if anyone can help me get a visitor's pass or give me some directions on where to go/what to do. If you want more information about me ask for my e-mail in the comments.

Thanks, Dimitris