Re: Toshiba Satellite A100 Key pad..
An external USB is the easiest. You can definately replace the keyboard for cheap, i think i see them on average around 30 to 50 bucks. Probably could get a used one off ebay for less than 20 bucks. The issue is it is an absolute pain to do anything with a laptop aside from replacing RAM and hard drives.
It is doable, just realize that you will have to take apart most of the laptop to release the keyboard. Then you have to be gentle because the ribbon cable is really fragile.