Many video games have deep storylines. This has been the case since the early text adventures where creative writing was all that existed to keep a player engaged in the game. I believe that some stories are better served by this interactive medium rather than say a novelization or a movie script and I'd love to give it a try, but without having any contacts in that industry or real experience working in that medium, I was wondering what it takes to get started? Find or start an open source game project? Send some kind of treatment to an established game publisher or developer?
My first advice is -- don't. There's an attitude in the gaming industry that working on games is so cool they shouldn't have to pay you a fair wage. Working conditions in the game industry tend to lag behind other sectors. Salaries for graphic artists and coders in the game industry are about 1/3 of what those same people would make in any other sector, and I suspect it is the same for writers.
If you must get into the game industry, though, find a company with a history of treating its people fairly, and that use an open-source engine under their games. The business argument for a company to use an open-source engine is persuasive, but for you as a writer the biggest difference is in corporate culture and willingness to give you a fair shake.
Once you've figured out who you want to work with, put together a proposal, send it in, and cross your fingers.
Bioware had a contest several years ago to hire a writer. Certainly not an appealing way to go about applying for a job, but that contest did leave behind some potentially useful tips for what sort of writing game companies might be looking for, eg:
Creating a Neverwinter Nights module would definitely be something you could do in order to get a feel for the flow of writing if you want to get involved in writing for RPGs.