Engage: sadly, I don't think your MacBook can work with any more RAM (well, maybe 3GB, but that's it). If I'm not mistaken that's a 2007 MacBook (white or black) with a very weak GPU that can't be upgraded, and a limit of 3GB of RAM.
Like any computer that is that old, what you really need is a new(er) one. The speech dictation function MIGHT work if you upgraded to Yosemite, but the overall experience would be really terrible as Yosemite is designed for at least 4GB of RAM and decent graphics. I upgraded to a 2012 MacBook Pro and put 16GB of RAM in it and the difference is nothing short of astonishing.