Assuming you're not using a "Homegroup" with Windows 7 (which uses TCP/IPv6), try disabling TCP/IPv6 in both the Windows and Mac Laptops in case that's causing the Windows Laptops to crash.
In Windows, open the Network Connections folder ("Start > Run", type NCPA.CPL and click OK), right click the Wireless Network Connection and select Properties. Untick the box for Internet Protocol Version 6 (TCP/IPv6)" and click OK.
In the Mac, go to "System Preferences > Network", select the wireless adapter and click the "Configure" button. In the TCP/IP section of the next box, click the "Configure IPv6" button at the bottom and set it to "Off". [I only have Mac OSX 10.4 so later versions may differ slightly.]