Patrick, I'm glad to see your enthusiasm to explore and expand on your computer knowledge. Unfortunately I have to be the first to let you know that in this case your ideas on upgrading your systems by simply changing the processors just won't work.
First of all a Pentium 4 (or Centrino, which is the mobile version) literally will not fit into any of the systems you mention. All CPUs are made in specific form factors to fit into different sockets. Most Pentium 4 processors were made for Socket 478 or 478B sockets, which mean they have 478 pins on a chip roughly an inch and a quarter square. The high number of pins allow more signals and data to be passed simultaneously to the motherboard, one way the speed of the CPU operations were increased. Pentium III and older Celerons were mainly socket 370 chips on a chip almost an inch and three quarters square. The lesser number of pins were aligned in six concentric rows with a blank central square. Pentium II and even older Celerons used Socket 7 and any of a half dozen other schemes and were often put on daughtercards to make them somewhat interchangeable. It would be like trying to put a square peg in a round hole.
They also make other forms, like socket 775, 939, and the newest AM2, all of which are pin-incompatible. In certain situations there are adapters that will let you put a newer CPU into an older socket but the specific upgrades you mention have no equivalent.
There are other engineering factors to be considered as well. Not all CPUs run on the same voltage. Many desktop motherboards have been designed that are adjustable either by selecting the operating speed with jumpers (old style) or by electrically sensing the optimum speed of the CPU. Then there are the memory and bus speeds. The CPU has to be able to interact with the memory so they must share a signal speed. This is the Front Side Bus. Older Pentium 4 CPUs were designed to use PC-133 memory but more powerful CPUs. certainly any in the 2.0GHz and up range, are designed for Double Data Rate (DDR), which is PC-2100 up to PC-3200. The pin configuration of the memory is different also to reflect and optimize the faster design. Of course there is now a DDR2 design and most recently DDR3. Core-Duos and Quads use the DDR2 and DDR3 type memory.
Another factor is heat. Faster CPUs run hotter. the system must be designed to accomodate and release the greater amount of heat generated, thus there are larger heatsinks and fans and more vent holes. Otherwise the CPU would start acting erratically and eventually burn out.
Things would be slightly different if you were talking AMD chips, as the socket 472 was much more versitile and could handle a wider range of CPUs and speed, from Duron to Sempron to Athlon XP, all because of the way AMD designed their chips. Of course, they too had to upgrade to surpass physical limitations, leading to the socket 754 and other newer designs.
Desktop machines are much more flexible to upgrade because of the space available and the fact they are designed with expansion slots. If you need a higher video card to run games, or more com ports to run extra printers or whatever, you can generally place a card in a slot to add the functionality. If you reach the design limits of a motherboard you can usually swap it out. Not so with laptops.
Laptops in particular are hard to upgrade because everything is integrated into or designed to plug into the motherboard, which has to fit the case properly like a jigsaw puzzle. This is not to say it is impossible to upgrade somewhat, but usually for laptops it means putting a faster CPU of the same form. Here is an example that is specifically for the IBM T40 laptop:
No, if you want to upgrade to Pentium 4 or Core Duo or Core Quad speed and performance, you will have to go out and buy a laptop.
Please do not let this discourage your enthusiasm. You share the spirit of the old school to push the limits that has made all of these computer evolutions possible. Consider formal training to round out your knowledge and to expose you to more within the field.