Awesome! You handle that stuff, I'll get the bones of the VR sim written out.
I'm also happy to help with voice-acting - I'm thinking that it might be good to have the mech's internal systems 'speak' to the player from time to time (y'know, "Main System - Engaging Combat Mode" when the player enters it, "Armour Levels Critical" when the player hits 20% HP, "Ammunition Depleted" when the player's weapons are empty, etc.).
To cover things now -
Are we running with Fallout 3 as a requirement or not? Eg, can we use Fallout 3 resources?
What kind of feel do you want to go for with the VR sim? A high-end mech shooter, or basically New Vegas with mechs?
How lore-friendly do we want this to be?
Should the VR sim be something the computer constructed of its own accord (very mechanical in nature), something constructed by a post-apocalyptic group (using the Mojave as a worldspace), or an Operation: Anchorage-style training simulator (the player's thrown into a battlefield used to train US Army soldiers)?
On the subject of concept, I have this awesome picture in my head of a blend between the two - basically, a Capital Wasteland-esque landscape (incredibly heavily destroyed, rubble everywhere, etc.) where all major factions are much more heavily-armed (Vertibirds everywhere, power armour is standard infantry issue, mechs are of moderate commonality, etc.). Possibly mentioned as being the US Military's post-apocalyptic VR sim if the nuclear war had happened in 2100 instead of 2077.