I'd like to try and roleplay my first run through of the game. I'm not a big fan of how these games through you in the middle of the world you supposedly live in but don't give you enough information to really understand what is going on. I'm hoping some of you can give me a little more information on the world we live in.

Here is what I learned from the opening:
I work for the Mojave Express as a courier.
I was sent to New Vegas to make a delivery.
The NCR controls the western side of the Hoover Dam.
Ceaser's legion appears to control the eastern side of the Dam.

This is where my logic takes me. Please let me know where I might encounter problems with it.

It could be assumed that the Mojave Express primarily caters to making deliveries in and around the Mojave desert. The Mojave desert primarily occupies southeast California, the tip of Nevada, and Northwest Arizona. Pretty much everything to the Hoover Dam, including New Vegas. Since the NCR controls Hoover damn, they must control all the territory between there and California. I'm willing to accept that New Vegas may not be under their control and is instead an independent territory. However, Goodsprings and Primm should both be part of the NCR.

Seeing as I was working for the Mojave Express, that would imply that I was more than likely a citizen of the NCR.

Without really giving any of the story away, am I missing anything obvious, or heading down the wrong path of logic?

Not bad, it's pretty complicated, yes.
They are both at the extreme edge of their territories, and NCR has camps, and are not all over the place everywhere.
Most folks around regard the NCR as the lesser of two evils...
Everyone just wants to mostly remain independant, but they are scared of Caesar so maybe the NCR isn't such a bad thing afterall.
Nobody likes Government until one day they need protection, heheh...
Regards