I am redesigning a website to better work with mobile devices. My problem is that on the right side of the page there is an open space, even though all the specified widths are the same. Here is the page: http://uniqueantiqueskingsport.com/wp7. So far I have only tested it with the Windows Phone 7 emulator.
I don't have a WP7 to test this on, but I'm seeing the same when viewing on desktop browsers. The problem is your footer content, a lot of it is set at
margin: x and
padding: x. Those margins are adding to the box model of your content, and forcing the page to expand.
Read up on the box model at Sitepoint's awesome reference site.
For the record, IE9 on Mango automatically zooms to fit the width of your content. But using a dynamic width would be much better.