I was thinking about looking into the Fallout license at one point, but I was warned how much a hassle licenses can be (and expensive) .
This seems like odd timing and an a odd choice. I know I'll buy it because I love PA and fallout, but at this point, it seems like a bad idea to make it d20 modern.
First, wizards seems to be ramping down it's d20 modern support. Second, 4th edition seems not to far out. And 3rd, there's a number of PA d20 games.
I would have gone with a new system, perhaps something close to the crpg system (although there is already an official pnp system for fallout out there somewhere).
It's odd that I've never heard of this yet and I'm pretty plugged into all things PA.
-chris