Indeed, http://www.crucial.com/store/listparts.aspx?model=Satellite%20A100-259&Cat=RAM shows it should work. And it doesn't. Time to contact Toshiba customer service, I'd say.
I have a Toshiba Satellite A100-259 laptop and I want to upgrade the RAM from 1gb to 2gb, which is supported by this laptop. Problem is the laptop will not boot up after I have installed the new RAM, instead it starts up for a few seconds and turns off again, it then repeats this process about 5 - 6 times before switching off totally. I initially thought the RAM wasn't compatible but when I put one of the new 1gb RAM modules in with one of the original 512mb modules the laptop boots up fine and shows 1.37gb of RAM available (I presume remainder of RAM is used for graphics). I can change the 1gb module with the other 1gb module and laptop still boots fine, proving that the new 1gb RAM modules work in this laptop independently, they will just not work together. Bios has been updated, so I have absolutely no idea why the new RAM will not allow my laptop to boot up. Any ideas and / or solutions to this would be greatly appreciated.