Unfortunately I can’t do a lot to help you with this. Because:
(a) I got into the industry by them coming after me, not the other way around. The first time, it was for Star Trek (Star Trek: The Kobayashi Alternative), and as far as I can tell, the guys at the company that Simon & Schuster Interactive hired on to handle the coding side of things said to each other, “Let’s hire the best Trek writer we can find to do this.” And at the time, they felt that was me. So they called my agent and hired me and I worked with them happily for about four months, and we wrestled the thing into the can, and everybody was happy.
And the second time, it was Privateer II: The Darkening, and as far as I can tell, Erin Roberts at Electronic Arts said to the guys on his team, “Let’s hire a good SF writer who’s also done some game work and has at least ten years or so of screenwriting experience to write this game, which is halfway to being an interactive movie.” And at the time, they called around and talked to various agents, my London agent among them, and they decided the person they wanted was me. So they called her and hired me and I worked with them happily for about six months, and we wrestled the thing into the can (it being the LONGEST goddamn screenplay I have ever written and memorable just for that), and everybody was happy. (Well, except for all the people who always felt afterwards that the game engine was still a little buggy when release date rolled around.)
I think you may see a pattern emerging here.*
And this is the source of the problem I have with advising you. Because of all this coming-after-me, I am completely lacking in any useful data on how to get into the business yourself. It’s annoying, but if I said I had the slightest idea of how you might get started, I’d be telling you a lie.
And now we come to reason (b). Even if I had purposely gone looking for this kind of work, back in the day, the industry and the way it works have changed so profoundly since I wrote my last game that anything I know, or knew, about the process would by now be totally useless.
If I were in your position, I would seek out someone who’s done more recent work and has an online presence. Rhianna Pratchett comes immediately to mind. Rhianna has been right around the block, in terms of games writing. She’s got a whole heap of interviews linked to at her website; if I were you I’d read through them carefully and see if she has something to say about the how-to-get-in end of things, because she’s beyond knowledgeable about this stuff.
Sorry I can’t be of more help to you. Good luck in your search!
ETA: And Rhianna suggests that you look at these:
Richard Dansky: On Becoming A Game Writer
For more general info: The International Game Developers’ Association Game Writing SIG
*There hasn’t been a third time. Yet. But that’s only because people keep making me write these damn miniseries. I would love to write another game some one of these days. Maybe somebody in the business will see this and come after me. :) But not right this minute please.