Need more specific info on the your current CPU or motherboard.
Pentium 4 2.4Ghz could mean either:
Pentium 4 2.6Ghz Northwood 130NM 1.525V & 58.9W TDP
Pentium 4 2.6Ghz Prescott 90nm 1.25/1.4V & 89W TDP
or maybe even something else.
Pentium 4 3.2Ghz CPU is probably a Prescott. Just need to the motherboard data to be able to check if they work together.
You can use CPU-z utility program
to get the motherboard/mainboard details. Of you can use the Dell support site to find the answer there.