Another one of Jed's Pet Peeves:
To forgo is to do without. "I will forgo a trial." The for part is the same as in forbid or forswear; its meanings have to do with "going against" or "excluding" or "prohibiting" something.
To forego is to go before; the word has almost no common uses. It appears mostly in inflected form: a foregone conclusion is one which is decided in advance. "The trial's outcome is a foregone conclusion." The fore part is the same as in before, or the fore of a ship.
A foreword is an introduction: a "word" that goes at the fore of the book. There's no such word as "forword."
The confusing thing is that the for in forward actually derives from fore—it means more or less "toward the fore." In Old English it was spelled foreweard.
The other confusing thing is that forego has acquired a secondary meaning: it's now listed in MW10 as a variant spelling of forgo. So this is really another case where one of my spelling peeves just hasn't caught up to common usage. If the dictionary accepts forego, I suppose I too must forgo my objections. But it irks me.