Vista - Pentium M not stepping down - Heat issues

When I installed Vista RC1, I noticed that my Dell Inspiron 8600 ran hot -
the fans are always starting and stopping. Looking at the task manager, I
found the CPU usage negligable, so I looked elsewhere. When I installed
i8kfangui, I noticed that Vista never steps down the CPU to 600 MHZ, so it's
always running at the full 1.7GHz. Has anyone found a fix for this? I'd
like to use Vista full time, but can't until this is resolved - too loud for
the classroom at college.

I have already checked my BIOS version - A14, which is the newest. I'm
looking at reinstalling to see if something got corrupted along the way but
hoping that someone knows a fix before I do that.

Thanks in advance!!
-Derek