To avoid the foibles of the Tiscali installation disc, connect the computerto router via an ethernet cable and address the router's user interface directly from Internet Explorer.
Router IP address is probably 192.168.0.1 (you can check this from the Command Prompt in Windows, typing ipconfig /all).
Router's Login Username is admin -- and Password is probably admin or password. Under wireless settings you will be able to select the encryption method manually.
When connecting a new computer, usually simplest to disable encryption temporarily until you have a reliable link.