This sounds like a proxy server problem, but why this should only occur on the wireless connections is a little mysterious.
Can your browse to 188.8.131.52 (which is google) from your wireless connected PC. If this works and google.co.uk doesn't then we will know a bit more about your problem.
On the PC's:
In Network Connections, is the TCP/IP configuration the same for the Local Area Connection and the Wireless Network Connection?