Hello Dainslef,
First of all, Welcome to the Discussion forums!
Unfortunately, there are no official tours of Apple Headquarters. There is an Apple "Company" Store located at their HQ that one can visit that sells some items that are not sold at the normal Apple Stores (such as Apple logo products such as t-shirts and the like I believe). The headquarters are located about 45 minutes outside of San Francisco, CA.
All contact info for Apple can be found at
http://www.apple.com/contact/
The address for the Apple Headquarters is One Infinite Loop Cupertino, CA
littleshoulders 🙂