Probably the most important reason for new employee orientation is to ensure that the new employee is fully productive as soon as possible. This benefits everyone -- the employee; the employee's work group/manager; the company -- even the employee's family! A fully productive, competent employee will be confident and less stressed both on the job and at home.
Sometimes "orientation" is also called "onboarding".... The "process" needs to make sure that the new employee knows everything he/she needs to know about the job, the company just as soon possible.
Everything..... policies, procedures, sacred cows, how to get stuff, what kind of "stuff" he or she can/should have; who does what; where to get help, stuff, supplies.... Everything! An new employee internal intranet is a perfect knowledge source...
If you need some help creating an intranet, I'd be delighted to offer my services to you. I've done a couple of them for larger organizations.
For those that are interest in getting into orientation in some depth, I started a Yahoo!group discussion forum on Orientation a few years ago --
http://groups.yahoo.com/group/orientation/.
Cheers