The Dell 2400 was their lowest end Budget basic machine a few years ago. Power supply is limited. Memory slots are limited. CPU cooling system is limited. Why, why do you want to do this with an old machine having limited memory. You will have problems with power supply and upgrades of other components.
It can be done, but everything will run at the speed of the lowest component, so you gain nothing. You will need to replace the cpu fan and heat sink. That machine doesn't even have an AGP video graphics slot, as I recall, nor a PCI-Express.
Putting a faster CPU in a slow motherboard does nothing useful unless the old 2.4 GHz 400 MHz FSB is damaged or burned out. I can just about guarantee you will not detect a faster operating system in that old truck.