P-M & P4-M are not the same chip.
If your laptop uses P4-M you can't fit a P-M into it.

Also verify how far you can u/g the processor re speed:
o BIOS upgrades will take you quite a way
o However, h/w board revision can be a factor

The best upgrade for a laptop is to go from say a P4-Celeron 2.0Ghz
to a P4-2.66Ghz for example. Within a range, eg, P4-M, you are only
going to get the benefit of a few hundred Mhz. If you find it is the HD
that is slowing you down, consider fitting a Hitachi 7200rpm - your old
HD may well be 4200rpm which is slower on latency & peak transfer.

Re 2.4Ghz v 2.5Ghz, for the 200$ you could buy a faster HD for example.
Depending on your application, that may be more noticeable than the CPU.
--
Dorothy Bradbury
www.stores.ebay.co.uk/panaflofan for quiet Panaflo fans & other items
www.dorothybradbury.co.uk (free delivery)