Most Pentium 4 chips on the LGA775 socket are Prescott based. I'm not sure if Intel ever released Northwood based LGA775 chips, I doubt it.
In other words there's no difference between both chips you are mentioning unless the 1st one is in a Socket-478 format (the old one) & the second in a LGA775 format (the new one).
Do you have any links to the chips you're talking about ?