According to my knowledge, and the package mechancial specifications in the datasheets, the Intel Celeron M 420 (SL8VZ)
processor is 65nm, Socket 478 Micro-FCPGA.
The Mobile Intel Pentium 4 (SL6FH)
processor is also Socket 478 Micro-FCPGA.
How have you identified the processor you currently have? I'm in the process of upgrading my laptop processor, and when I use CPU-Z
to verify the specs of my Intel Celeron M 430 processor, it shows it as being Socket 479 m-PGA...whereas The Intel Celeron M (65nm) datasheet state that the Intel Celeron M 430 processor is available only in 478 pin Micro-FCPGA and 479 ball Micro-PCBGA, and the actual socket on my laptop's motherboard says s478.
The best thing to do is to physically take a look at the socket on the motherboard and the pins on the processor itself.