This is how
The Register describes the announcement of the name:
Microsoft finally dropped the Longhorn moniker today
and “revealed” that its next generation client
operating system will be known as Vista when it ships
next year.
...
The corporate video accompanying the announcement
went some way to filling in the details. It seems
using Vista will, at last, enable you to: sit in front
of a computer, show someone your tablet PC, show
someone else your mobile phone, get into cars while
carrying a laptop and walk through sun-soaked rooms
with highly polished floors, even while being buffeted
by pulses of multicoloured light.