Control Panel > Regional & Language Options > Language tab > Details button > under Installed Services, select/highlight Keyboards, then hit the Add button on the right. Scroll down to pick United Kingdom, then hit OK. Then remove US. That should do it. Then keep hitting OK til all your windows are closed. Done.
Tom
The UK keyboard has the @ key at a different place, near the return key, it also has the £ on Shift-3 and a few other non-letter keys are in different places, I personally prefer the layout as I've been using it for 8 years.