[Ankesh]

Does the car dealer's website have a RSS feed? (good chance of this)
Or does it have any sort of an API? (unlikely)

If yes - this would be easy.

If not - then its still possible - but you'll have to hire a developer to create a script / macro that would scrap the listings every day or week.

If you don't know what a RSS feed is - let me know the website URL of the car dealers and I'll let you know if they have a RSS feed or not. Most content management systems that websites are built on with these days come with the RSS feature.