IE7's zoom is shaky at the best of times and I wouldn't waste too much time on it because it has many many bugs. It is never going to look exactly the same :).
I can tell you though that the problem is cause by position relative on your #container_top (probably) which throws IEs zoom out of wack. If you remove the position relative from #container_top then it will zoom a lot better, perhaps. I'm unable to do any testing because of my location however
Position relative on main containers seem to screw up IE7's zoom, as well as auto margins on the <body> (along with other things)
There's just too many bugs to reliably try and fix it. As long as you can read the page on zoom in IE7 don't worry about anythign else
I hope this helps