Trouble With a Stylesheet in IE6 (surprise surprise)

I’m awful with layout (my site’s stylesheet will attest to that) and really can’t figure out why, since Microsoft released IE 6, I have a button out of alignment. I have the same problem when using Opera or Safari but, because the problem was not huge and the browsers aren’t widely used, I decided to leave it. And then IE6 happened.

The site is Old World Wandering. I’ve made the stylesheet available here as I couldn’t be sure that it wasn’t already.

I know this a painful, niggly question (and I’m already half expecting you to ignore it) but a little help would be much appreciated.