I'm with Marcus on this one, the problem is not with IE7, it's with the way the website behaves in IE7! Incidentally Marcus, I'm not sure IE7 takeup is quite that high yet, but 30% of the visitors to our site last week were using it.
A little surprising that it works in Firefox but not in IE7. Any suggestions? Well, maybe one of our experts will pass by soon, but my suggestion would be to ask your web creator to fix the problem; or find someone who can!!
Hope that helps a little.