I have a PIII 900
Its not soldered on, cause that would increase production costs, plus if you fry your MOBO your manufacturer would most likely wanna give you a new MOBO and use your old CPU as opposed to replacing everything if it was soldered on. Anywhoo, yanked up my PIII 700 and dropped in a celeron 1.13 and gained 1000 points on PC mark. Went from 2332 to 3332. Not to shabby you would think, make sure you find out what kinda socket, BGA of micro-PGA. No point buing a new CPU without being able to stuff it in there.
Also replase the thermal paste with AS3 when you take it apart, i did and now my fan turns on once an hour as opposed to every 15 minutes.
I have an IBM T22 900, i put 700 above because thats what it runs at on batery and thats how i use it most of the time.
Good Luck friend and ejoy your laptops new found power.
Kam