I think you've been there before.
This post has a site which is different in FFox and IE7. I have been trying to help but CSVista has let me down with this one. As my knowledge of CSS is very rudimentary, I wanted to use IE7's web dev program to alter the css to see if I could do any better.
According to CSSVista, I had sorted it out, but it was not so. Well, If at first you don't succeed, try, try ....It's very trying. It seemed such a simple problem.
Back to the drawing board.