Including our ancient Domain Controller, We have 6 PC's here at the house, all accessing the Internet through the same router and cable modem. All have their security levels, network configurations, and Internet options set the same. None has any trouble accessing any other website that we have tried. Here's how ability to access the High Performance Stangs site breaks down by PC:

Domain Controller running Win 2000 Server ................ YES

Old Vista laptop running Vista Business 32-bit ............ YES

File and media server running Win7 Ultimate 32-bit ...... NO

My desktop workstation running Win7 Pro 64-bit ......... YES

Wife's desktop workstation running Win7 Pro 64-bit ..... NO

My notebook running Win7 Ultimate 64-bit ................. YES

As mentioned by OP, inability to access the site is not browser dependent.

Further, those PC's which can access the site in a browser window are consistently able to receive replies when pinging the site from a command prompt. Pings from those that cannot access the site in a browser window all time out.

Maybe, this data will help us all figure out what's going on.