There are several training programs available for Microsoft Office products:

Microsoft has some basic training online here.

Alison has some training here.

GCFLearnFree.org has training here.

And Lynda.com offers training here.

 

Microsoft offers the Microsoft Office Specialist (MOS) certification.  

Microsoft estimates that MOS certified entry-level business employees may earn up to $16,000 more in annual salary than their uncertified peers.

Certification from Microsoft on their Office products is conducted by Certiport.  Visit their site to find a testing center and schedule an appointment.  They do charge for this, and pricing varies between locations.