Well, it really depends a great deal on how you define "God". That being said, no, one probably cannot disprove the existence of God, so long as the definition of "God" is even slightly clever.
Of course, that's a bit of a slender reed upon which to hang one's faith. Not being able to disprove something isn't much of a reason, in and of itself, to believe it's true - the believer will probably wish to seek something a bit more substantial than just that. After all, I can't disprove the existence of Santa Claus either, but that's probably not quite enough to persuade you to believe in him ;)
Where a thing can neither be proved nor disproved, it has been proven to be a matter of faith.
I don't know if you really need to prove such a thing - it's pretty much true by definition...
I don't know if you really need to prove such a thing - it's pretty much true by definition...-you-
If that is the case then you must agree that atheism is based on faith, not reason.