By right, you shouldn’t get both horizontal and vertical scrollbars unless you make the content large enough to require them.

Howeve typically due to a bug in IE, this happens at times.

IE6-7 (amongst other browsers) supports the proposed CSS3 extension to set scrollbars independently, which you could use to suppress the vertical scrollbar:

overflow: auto;
overflow-y: hidden;

You may also need to add the following for IE8:

-ms-overflow-y: hidden;