pentium 4, 1.7ghz. I want to use the same dell dimension 4400 motherbooard
Your motherboard is a 478 socket motherboard. I suggest P4 3.0 Ghz - for the best value of this cpu I would take the refurbished which means that the reseller has made sure that the chip is working.
I have connected dell and they say that no cpu upgrade is possible however they couldn't precise on why it couldn't; it's either bios restriction or too low psu or both. P4 2.53GHz - I read that the 3.0 won't but maybe this model.
You have to try.
Investing in this computer is not worth it. I would rather spend around 300 and get a whole new system.