Disabling Trackpointer Dynamically

[MWET40]

I have a T40 that is almost 5 years old. 95% of the time, it is docked and I use a keyboard and mouse connected to the dock. So even though I am a touch typist with (egads!) 45 years of typing experience, I still find the T40's keyboard a bit awkward for that 5% when the T40 is a true laptop. Try and I will, I can not cleanly hit the g, h and b keys without occasionally brushing the trackpointer and having the subsequent text be inserted in some incorrect location. Since I use a USB mouse almost all the time when using the T40 as a true laptop, I have disabled the trackpointer and use the navpad when I do not use the mouse. It works fine, but since the trackpointer has utility too, what I would prefer is to leave the trackpointer enabled and have it automatically disabled when the system senses a normal mouse in a USB slot.

Any ideas re how to do this?

Thanks