Vista - Can't use steedstep on Pentium 4m

I have an Inspiron 8500 with a 2.2ghz Pentium 4m processor, I dual boot
between Vista and XP. In XP, speed step works fine, but in Vista it doesn't
no matter what I do.

I prefer Vista, but it really kills my battery life running at full speed
all the time ... runs hotter and the fan runs a lot more.

I've set it up to balanced under power options. I've tried 3rd party
applications like rmclock, but either they're XP only or don't support the
P4m. No vista chipset drivers for the 845 on Intel's web site, it uses the
included Microsoft drivers, perhaps they've decided it wasn't supporting this
feature in my chip? I've tried SP1 with no improvement.

Anyone have any ideas or a 3rd party application that will work or a driver
or something to get it to work?