I upgraded my Dell XPS M1210 from Windows XP Pro to Windows Vista Business about 3 months ago.  I never had any problems of this nature in all the time using XP but now, more often than not, if I'm using battery power and plug the laptop in, it locks the entire thing up.  I've tried plugging in the power end and the notebook end first to the same end.  I would guess this happens around 4 out of 5 times I plug it in.  The only way to fix this when it happens is to hold down the power button to shut down and restart.  I've upgraded all of my drivers to Vista versions as well as Dell Quickset and none of this has changed anything.  I'm guessing this may be an issue with power management settings between battery and AC use but I wouldn't know what.  However, in all the time I've been using Vista, this has never happened when switching from AC to battery, only battery to AC.