I am a newby and need to know what ratio I can make my screen. The size of wall I have is about 6 feet wide by 3 1/2 feet tall. What is the exact dimension I can use?

If it matters, my projector I'm thinking of buying is this:
Panasonic PTAE1000U
1080P HDTV Projector

http://www.costco.com/Browse/Product.aspx?Prodid=11195982&whse=BC&topnav=

First off you are looking at a pretty limited space for a screen, but assuming you could use your entire wall height with a 2 1/4 inch border for a screen and I am doing my math correctly. Your screen viewing size would be 66.67"x 37.5" and your entire screen size with the border would be 71.16" x 42. Also I don't think you are allowed to post the link you just did.