Android - How to change calendar week start day in Android?
This is apparently not possible on a Motorola Droid with Android 2.1.
FroYo is slated to release next week. Maybe it will also change the ability to set this value. (If it does I'll change this answer.)
Sadly, this is still not possible with Android 2.2 either.
I'm not exactly sure whether it's the same on general Android as my have a Hero with Sense but on my phone it's:
Open Calendar/Press Menu Key/ Press More/ Settings/Calendar View Settings/First day of the Week
The popular home screen replacement LauncherPro Plus comes with a home screen widget that does just this and sync's with your Google calendar