A couple questions on replacing cpu

First of all would it be worth it going from a 2.0GHz 400fb to a 2.40GHZ/512/533 CPU Would there be a noticeable difference. I'm not even sure my P4VMM2 mobo will even take that cpu. On another PC, our kids, needs a cpu so I was going to get a faster one for me, and install the 2.0 GHz 400 fb in there because that is the fastest the mobo will take. I upgraded my PC to 1 G of DDR ram and 128 video card. Also is it much at all to change the cpu other than replacing the thermal compound.
A year old and the bios went bad on the heat sensor for the cpu so I hook the fan up direct. To my undestanding this is what some builders will do to keep the pc cool. Thanks,

 

If you mean that the bios controlled your fan speed based on a heat sensor, to be honest, I've never seen that before.

If that were an option, I can tell you that I would never use it. Hook your fan directly to the power supply and let it fly either at 100% or in the past, I've had cpu fans with a pot attached that let me tweak the speed with a knob.

I wouldn't trust my fan speed to software though.

Gary