I have had Kinkos print 10ft banners for my company at a very reasonable price.

I have to agree that Photoshop/In Design or Corel Draw (my personal favorite) would be the best choice. However, if you don't have access to those, Open Office has a word processor that does not have the page size limitations that MS Word has. I have used it to make layouts as large as 5ft and I'm pretty sure that it will go larger. And Open Office is a free download! With Open Office you can save the file in any format that your local print shop will accept. (doc, pdf, etc)

No, I don't work for Sun Microsystems they just make a good product that is FREE!