There might be many different options for you to upgrade or replace your processor with. We recommend contacting the computer manufacturer as they have set the valid compatibility list between the computer, the BIOS and the available processors in the market. The system manufacturer should also provide the specifications on what technologies from the processor might or might not be supported.
Please bear in mind that what limits the compatibility is the computer itself (motherboard and bios) not the processor. The motherboard requires to have the proper micro code to manage the processor, if not, the system will not work, and it is the computer manufacturer or Original Equipment Manufacturer who develops the BIOS to include the microcode for the processor
I have definitive answers for some of the questions in my original post. Gateway ML6xxx, MT6xxx and NX5xxx with an Intel 943GML Chipset can be upgraded from the Celeron M to a T7200 or T7400. I have tried both CPU`s in these three budget notebooks,and the results were remarkable,
Stock from the factory these machines had Celeron M`s and either 512MB or 1GB of RAM, they were slow and labored heavily if you try to multitask, but with 2GB of ram (max) and a T7200 they come to life performing like higher-end machines. I didn`t see a big difference in performance between the T7200 and the T7400, I believe the price difference makes the T7200 a better choice.
Most people won`t consider this information on four year old machines interesting or relevant, but if your reading this you are probably on a budget. If you need a cheap, fast, dependable notebook for less than 100 bucks this set is hard to beat.