Martin, you can check the version of IE by clicking HELP>About.

If on IE6, do you have a search button below the menu at all? If you do, click that, then in the left hand panel that opens, click customize, and you should be able to select Google there.

If you can't do that, then Tiscali probably customise IE when you install them as an ISP, which can still be gotten around, but would probably mean changing something in the registry - can be done, you just need to be careful when doing so.