The multiple-key-press issue is not software related. It's hardware related. Pressing too many keys simultaneously overloads the channel, and you'll either get ghost-key responses, or missing responses.
I'm not sure what you would do in typing that would require you to hold down four keys at once. Aside from gaming, or using editors, there's not much reason to (unless you have some funky key-binds setup in your word processor).
If you can't get around this (either by process or dexterity) I would suggest switching to another keyboard. I use a MS Natural Elite, and only encounter this problem if I'm pressing more than 5 keys at once...which is tough since each of my hands only has 5 fingers.