Connect to IIS on intranet from OSX

I have a Windows IIS server on my intranet that I'm able to connect to from my PCs as well as my MacBook running Fusion. But I am unable to connect to that IIS server from OSX.

I can ping the IIS web site's IP address in Terminal (e.g. ping 192.168.15.4).
And I can connect to the Cisco router (e.g. http://192.168.15.1) from Safari and FF to configure router settings.

But I am unable to connect to the IIS web site http://192.168.15.4 (or http://192.168.15.4:80) from Safari or FF.

Clicking around randomly didn't seem to solve the problem. I'm hoping somebody might be able to point me in the right direction.