Ads make left-hand column jump down

I’m very unhappy that readers using IE6 find that the left-hand column of my wordpress weblog https://intheboatshed.net jumps down to the bottom of the page.

This doesn’t happen when I use the sidebar of Pal Nila unedited, but it does arise as soon as I use the Presentation widgets gizmo to insert ads.

It looks fine in IE7, Opera and Firefox. However, in IE6 running on Windows 2000 the whole thing looks dreadful.

I wouldn’t mind so much but the kind of people who read my weblog care a lot about appearances but at the same time tend to use older computers, operating systems and browsers.

If anyone could offer advice, I would be most grateful please.