Thanks for the images, but unfortunately nothing was showing any information regarding what you are using at work for DNS name resolution neither your machine nor the XP machine that is working and that's because you forgot the /all after the ipconfig
ipconfig /all
Now the other thing that you've discovered regarding a proxy server, if your browser is trying to use a proxy server that is non-existent then that can certainly be an issue.
In IE9 click the little gear thingie in the top right under the red x and choose internet options, then the Connections Tab, and the LAN settings button, uncheck all check boxes and OK your way back out of there and then close and reopen your browser.
As for the Cisco device, I let my CCNA expire back in 2003 so it's been a long time and I've never even heard of an IronPort, but as a general rule Cisco provides highly manageable routers with many tools, filters, access lists, etc., to support or prevent web access by any device inside it, so I suggest you talk to whoever is responsible for managing it and see if what you are seeing is normal regarding the IronPort Web Security splash screen