What are your current HDDs? PATA or SATA? If you have SATA drives then your migration will be easier. PATA is barely supported in latest mobos. For example:
THIS Biostar mobo does not support Parallel ATA drives.
And one more thing you need to have in mind is the P4 socket... is it Socket 478 or Socket 775. I suspect it is Socket 478 if it's older. So you need to search for a socket 478 mobo.
As you see there are many questions
Good luck
p.s. And Welcome to PCTechTalk