Best thing to do is:

Register two business names first.....and get a DBA (Doing Business As) form/number for both.
Then PAY the extra money (like $200 or so) to get it INCed. (only the one that will actually do sell something
Now buy everything and register everything under the one that is still DBA and not selling anything.
Lease everything and anything back to the other company that is selling things.
This helps you in multiple ways.
1) You get tax right offs on both and the inc one get more for depresiation of assets.
2) It protects you because if someone sues you, the company being sued ownes nothing, so they can't get anything
3) If you have to declare bankruptcy, it doesn't hurt YOUR credit and you aren't forced to liquidate any assests becuase the company doesn't own anything.
Now that you have the two companies setup; you will need to find an accountant and an attorney.
(KEEP EVERY RECEIPT FOR EVERYTHING AND ANYTHING even if you didn't really buy it for either company; your accountant can figure out the rest.)
4) If you want to go on line, register your domain name, setup your web site, etc.....
---put the credit card processing gateway in the name of the INCed company though (liablility reasons)
5) Begin advertising and selling your products/services!
6) have a business account for both companies. pay the DBA company a monthly fee for the leasing of all items, etc.....
7) Do it right and you can show 5 years of loss while still making money! Tax Deductions (accountant's problem again! LOL)

and the most important thing of all!......Hire me to build your website! LOL no serously.....we can setup a e-commerce store with real time credit card processing and shipment tracking, etc, etc, etc....what ever you want or need it to do!

What do you have in mind to do? sell/service????? Just Courous...... Spend the majority in the begining on good advertising though!

The best tip of all though is research EVERYTHING!!!!!!! Good luck and wish you the best.