It's not that hard, usually you can get started by tweeking other peoples code that is available for free on the internet. Mind you I've been writing computer code since I was a teenager so to me it's second nature.
@Kayos have you considered listening to the CanBus ? I'd imagine the beemer will be using one and there will be loads of interesting data on there or are you wanting to be independent of the cars systems ?
The CanBus module I've played with is the MCP2515, it's a SPI so only 3 wires if I remember correctly.
