My core 2 duo t5300 seems to need the module "speedstep-lib" to be loaded. There are probably nicer ways to do this, but adding
to the file /etc/rc.d/rc.local should make sure the module is loaded each time you start the system.
Isn't it better to add it to /etc/rc.modules? That file seems set up to allow easy addition of needed modules. I added /sbin/modprobe thinkpad_acpi to it to get the thinkpad_acpi loaded for my Thinkpad.