Going about it the wrong way I think... this notion of getting an xbox to run a compiled FPSC exe.
If you really want to do it, I'd suggest writing an app in Unity that could read the FPSC map format and place the static and dynamic objects where you intended them to be as a first step (you would of course need to convert the FPSC models to FBX or other compatible format for Unity to be able to load them, but compared to what you're proposing, that's kid stuff).
Once you had that, then you could begin writing the game engine itself. The camera code, the code that lets you walk around, the code that lets you pick up a gun, pick up health, pick up items, shoot bad guys, the code that interprets FPI scripts...
... What's that? Sounds like alot of work? Yeah, well that's because it is. But unlike this silly idea of somehow magically running a Windows 32 binary on an XBox, you can actually download the source code to the FPSC game engine and use it as a guide for everything you would need Unity to do for you, which is about 1000% more help then you'd ever have trying to go about it the way you're proposing. A Unity interpreter for FPSC levels is theoretically possible to be created by mere mortals such as ourselves. Converting a windows executable of ANY sort to work on an XBox, let alone one that heavily employs the use of DirectX9 is on par with building your very own space shuttle in your garage on the weekends. You'll quite literally never get it off the ground.
Not trying to bust up the party, mind you, but I'm just trying to inject some reality into the situation. Best of luck, and if you can prove me wrong, by all means I'd love to see it.
It compiled! Ship it!
