Business Names: How to register "nationwide"?

[Crazy Cooter]

It's easy to register a business name in the State of Minnesota because you just fill out some paperwork.  From what I can tell, you could pick the exact same business name as someone else.  Pretty stupid if you ask me.

Anyhow, how do you register a business name that you can keep for yourself nationally?  If I started a business and called it Walt Disney, I think they'd come and shut me down no matter what I was selling.  The reason I ask is that one of my sisters wants to do some scrap booking ( ) sales/stuff online and we don't know how to go about "protecting" her name the way that Disney/AOL/Microsoft/3M etc does.

Do you trademark the name (like MAME) and that's it?  That seems like it's limited because you have to declare what category it is for.  Microsoft only sells software, but I doubt she could start "Microsoft Scrapbooking Supplies"... yet I could start a company called "MAME" that imported cars, and start unloading boats tomorrow.

I'm just confused how you lock down your name completely for a national consumer base.