|You kind of never know. On the surface exact spec memory ought to work but there have been reports of failure. Some OEM board makers may post that some memory is known to cause issues.|
In your case you can't get 2100 so you have to move up to 2700 or more to get a stick. If the bios fails to read the slowest ram and set it for that you could be in trouble. Generally the owners manual would tell how to populate the slots. This assumes that the board can support 1G (I assume it would). Also if you do have issues, the difference be 256 isn't that much since you are running it that way now. A 1G would be a fantastic improvement.
Text, talk, drive...CRASH.
Hang up and drive @#$%^^