I had a look in IE6 and it seems that all the menu on all pages off the front page disappear when you navigate to them.

I can't see why that happens but there are a couple of css errors though which may contribute.

1. In the (#nav li a) css style the background-repeat is set as "no repeat"
it should be "no-repeat"

2. between "form" style and "content.maintext" there are two closing tags }

Don't know if they are the cause but I will take a look at it in the morning again.