I discovered an odd thing with my Windows 7 box the other day: I can't ping it from any of my Linux boxes unless I ping them from the Windows box first. And by "I can't ping" I mean that there is no ICMP response received by the Linux boxes.
Windows tells me that the Windows Firewall is off, but I have spent the last few years avoiding supporting Windows so a lot of the networking UI in Windows is now strange and alien to me. The box is pretty new; it replaced a Windows 2000 box which died. I do most of my computing on Linux and really only need the Widnows for a small number of Windows-specific tasks, including my workplace's VPN.