The wireless should not make a difference,,,while on that subject do you have encryption set in the router....if not do that AFTER the network gets going.
go to control panel, double click network connections, then right click your network card , then click properties.
You should see tcp\ip , QOS packet share , microsoft client, file and print sharing
highlight tcp/ip, click properties
check to make sure the radio button "obtain ip address auto" is selected and that there is nothing in DNS. < only if you are using DHCP from the router>
Next go back to your network card in network connection, highlight and click on advanced , then network ident...halfway down you will see workgroup...both pc's this will have to match...click change to change on or both.
share a folder on both pc's
make sure the windows xp firewall is off
click start, then in run type ipconfig /all then press enter
what is the node type...usually says hybrid, actually anything but unknown
then type ipconfig /release wait for results
then ipconfig /renew