First, you mean the Dothan, not the prescott. Second, this depends on how the processor is connected to the motherboard. Hopefully, you have a socket-478 processor stuck in there, which means that you could just slap one in there, apply some AS5, and start praying. If your computer has a daughtercard for the processor, you can just swap that out with another daughtercard-if you can find one for the T41. If it's soldered to the motherboard, which many processors tend to be nowadays, you're out of luck-you need a new motherboard. If you can find one that fits in your laptop (and has the same display connector), you would also gain the benifits of a new motherboard anyway, including a better graphics card.
Out of curiousity, why do you want to upgrade?
And as a public service announcement-PLEASE TYPE LEGIBLY, AND WRITE MORE THAN ONE SENTENCE.
Thanks, and have a nice day!!