Well first, to register a company, you usuallly go through the state Secretary of State. However, I went to the site for MI and for the few minutes I spent there, it wasn't readily apparent. I did find this guide to starting a business in MI for you: http://ref.michigan.org/medc/services/startups/?m=12;7
Typcially what needs to happen is you register you company in the in which you live, aftter that, you go to the IRS website and you can get a Tax ID number for you company online. Once you have that, depending on the type of entity you have, you create organizational minutes (very easy) and take that to the bank with your tax id number, and start a business checking account.
Just my expereience from the last 4 I've done in Colorado.

