This happens to us if we are browser testing different configurations and leave the browser in a wrong setting. I'm on IE8 now so can't recall how to sort it in IE7. Here's a quick list of good/bad presentations of admin mode under IE8 configs in Browser mode/Document mode pairs:
IE8/Quirks mode Okay
IE8/IE7 standards Broken like your screenshot
IE8/IE8 standards Broken
IE8 compat/Quirks Okay
IE8/IE7 standards Broken like your screenshot
IE7/Quirks mode Okay
IE7/IE7 standards Broken
So, for some reason, if all other things are equal with our environment your browser is not going in to quirks mode.
I experienced something quite like it not to long ago. It turned out that the problem was a corrupt App_themes folder in the website.
I deleted the app_themes folder in the site, så the default app_themes in the EPiServer installation files was used in stead. That resolved the problem
Can't see the whole page in admin mode in IE with window 7.
Ex.
http://www.spasm-design.com/episerver/episerver_fail.png