Do you mean you want to change the keyboard layout from a foreign layout to English (UK) or is the entire operating system in a foreign language?
To change the keyboard, go to Contol Panel, Region and Language, Keyboards and Language, and if it is not already there, add the English UK keyboard and set it as default.
If the entire Operating System is in a foreign language, Windows Vista will have to be completely reinstalled. Depending on the installation media you have, this may mean purchasing an English version.