Strangely your site is not the only thing having an issue in explorer.
I just put Gallery 3 onto one of our intranet servers but I had real hassle staying logged in. Everytime I went to a different part of the menu it told me I was not logged in. I went thru directory permmissions, reinstalls and everything I could think of - no luck. Then I used firefox and everything works.
I tried cleaning the cookies on the machine and checking to see if I could post on the forum but it is a no go, unless I use Firefox. As we are not allowed to install any other web browser on a C2k system I am of course using portable firefox.