Umm, no Vista does not usually save battery power it usually
uses more unless you use manual or automated methods to
reduce the GUI effects, at which point it only uses a little
more instead of a lot more.

I get an extra 45 minutes when using Vista Ultimate instead of XP
Professional, with the Vista power management options having a lot
more scope than the simple XP ones.

Backlighting and unused features are usually controlled via a third-
party or manufacturer application, not directly via Windows.
Unfortunately when you wipe a laptop and install older operating
systems, you lose all of the manufacturer specific apps, most of which
are useless, granted, but some are necessary for power management.