While a mobile Pentium 4 (socket 478) can fit in a Pentium M socket (socket 479), the Pentium 4 is not electrically compatible with that socket. Regardless if the Pentium 4 is a mobile or desktop version, socket 479 will not provide enough wattage to power the P4 CPU. Addtionally, the laptop's BIOS would also have to be able to recognize the Pentium 4 CPU.
Although the Pentium M 750 is only 1.86GHz, it is actually more efficient at processing instructions than a Pentium 4. There are many reasons for this (which I can't remember), but one of the main reason was the shorter pipelines. The Pentium M 750 would be roughly equivalent to a 2.2GHz Pentium 4.