Need Help, Spell Check code

I'm working on an algorithm to do spell checking, and it's ok I guess. It doesn't seem to work as good as the ones built into popular programs though :( Basically, it looks at the word letter by letter, and builds a score based on the number of matching letters, non-matching, and also letters that are one place to the left or right of the correct place. It just has trouble with narrowing the choices down to as few as possible without eliminating the correct one. I'm begining to think I need to incorperate some general grammer rules or whatever. One thing I have noticed, is that the typical spell checker relies heavily on the first letter. So far, I have not put anything in to account for this at all, which may or may not kill its usefullness. If I come up with something good, I'll post a message. One big hitch so far though, is that it is slow, mainly because it has to load all the words first (over 100,000 of them). There really has to be a better way!