Using this guide you’ll be able to replace or upgrade the memory modules (RAM) in IBM ThinkPad T40, T40p, T41, T41p, T42, T42p series laptops.
In my case I’ll be working with a ThinkPad T41.
It came with 512MB RAM installed. There are two 256MB modules.
One of them can be easily accessed through the door on the bottom. The second module is hidden under the keyboard.