You'd have to use something like ClockGen to overclock it. That will only work if your notebook uses the same clock generator that the listed Pentium M motherboards use, if not (which will probably be the case) then I don't see any other option for doing so.
Do NOT get a TM4000. I had one and had a lot of trouble with it. It seems to be a problem with that particular line. Acer's support would not believe there was a problem with it.
I'd recommend a CL56 from Mwave. Its base price is currently $955 and you could do a lot to it with your budget.