I've been working today on a laptop Wireless set-up in which it could only be concluded that the on-board wireless of the Sony Vaio TR1 was faulty - or the driver wasn't man enough for the job.
I left the Client happy with a D-Link AirPlus 650 card instead of the on-board NIC singing like a canary.
But that's not your problem. I too would like to know what OS you are running the machines on. Because today, on an XP set-up, I had yet again to rebuild the LAN on the TR1 because it had been replaced by a bridge - to nowhere.
XP has done this several times to me. So the first step in troubleshooting this mixed LAN was to dispose of the Bridge and re-establish a normal LAN with the AirPlus adapter configured just like any other NIC.
So, if its XP, check the Network Connections for an unwanted bridge (I mean the System Configuration not the bits of wire). Check that your two wireless machines haven't reverted to an ad hoc arrangement. Check that the Router (I assume that this is also your WAP/DHCP Server) is using the same encryption as the two wireless machines.
Hope to hear from you soon. fobs