Firstly you can only do it on VISTA Ultimate and secondly the change
may not affect absolutely everything you see on your computer and for
the language to change on any applications installed they have to be
VISTA compliant for the language business.

That's not very technical but it sums up what I've seen here in
messages. I can't remember a specific part of Windows that someone said
did not change but it seems it's not perfect ..... surprised?

If I were you I would wait to install VISTA (especially if it's a
laptop) until a few months have gone by and everyone actually knows a
bit more -- and you might be able to get your English language version
by mail order or perhaps by downloading?