Welcome to the Webboards!!
One thing to be careful on is that the game builder (the editor) will only be for the mac (or so i've heard) and the engine (the little thingy that lets you play the game) will be for both. (or so i've heard)
Good luck with your game and I would start working on the plot/script for it as early as possible.
I doubt it will be years as it's already in Beta 3 (the third external testing phase if you are unfamiliar with the term) and was mostly designed (actually almost entirely) by Beenox (a fellow company)
Good Luck and Have Fun!!
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-TheDarkDragon
C M? M R Snakes.A R Not! O S A R! C M B D I's?
L I L B! A R Snakes! -President Bush talking to V.P. Richard Cheney at Camp David