I just solved a similar problem by disabling IPv6 on the server. The PIX was giving SYN timeouts in response to IExplorer traffic. It also would not allow pinging even though other W2K servers and XP computers on the network could ping through.
How do I disable IPv6 in Windows Vista and Windows Server 2008? - Windows Live Disable IPv6 in Windows Server 20008 Full & Core installation | Windows Reference