I just took a look in IE6 and 7 and they looked the same as my FF except IE showed some arrows... if those were going to be dropdowns or something...?
But I can comment on some other code if you want : ) Maybe post a screenshot of what you're seeing because mine I think are looking fine. Or did you fix it?
Your search form has a fieldset. Just a note: the XHTML specs seem to have no reason to deviate from the HTML4 specs as far as requiring a legend (so, technically your search form is legal without a legend), and since the reason for legends being required with fieldsets in HTML4 were a good enough idea, many consider it an oversight, and so keep the legends (and so because of this, little forms like search, I use some other block like div).
The main form on the page however does have actual errors. Multiple inputs have the same id and multiple for's have the same attribute. Also multiple elements have the same tabindex. Tabindex is kind of an evil when it screws with keyboarding (your form is pretty straightforward and people would tab in the correct order naturally, so tabindeces are doing only harm there). When I tab through the form, I'm unable to fill in any card details, and when it gets near Telephone on one column, it skips to the next column, then finally takes me back to the first col telephone, then the second... when multiple things have the same tabindex, I do not know that all browsers will act the same, since the idea is that only one thing has the tabindex of 1 on the page, only one thing has the tabindex of 2, and so on.
Just so you know, anyone who cannot load the images on that page for whatever reason, cannot use the menu. The Gilder-Levin method could cover images on and off both.