Site tested on several OSs and browsers. Unfortunately Microsoft, cavalier crackheads that they are, aren't one to follow CSS coding standards and as such have z:index issues. I've decided not to pursue this one any further, because to be honest if you use Internet Explorer I'd rather tell you to upgrade to the latest version and get patched http://www.microsoft.com/technet/security/bulletin/ms10-002.mspx as per recently highlighted security flaws.
Use Firefox. Use Chrome.