Scrollbar appears beside Control Panel in IE7

As per the description really. A couple of things to clarify;

All works OK in Firefox.
IE7 is fine when there's only one row of icons - I have the panel in the left sidebar (Garland theme) and using 24x24 icons they all fit side by side. No problem there.
IE7 is also fine when there's only one column - for example, using 48x48 icons, which means you can only get one in the sidebar at a time, and you therefore get one long column.

The problem arises when using, say, six 24x24 icons. Firefox renders it with no problem, but IE7 puts in a scrollbar beside the control panel, which only scrolls a pixel or so up and down. Do I need some sort of CSS hackery to get it to work properly?