Check out
Ravenloft: Fraternity of Shadows: Home of Ravenloft on the Net, and post this question on their
forums.
There are some intro threads stickied at the top of the general forum. Note that the site is also a veritable treasure trove of netbooks, gm resource, adventures, reviews and information on RL in general. Also check out their FAQ and the Mistipedia.
Another great site for netbooks is
www.kargatane.com. (The authors of this site, became the 3E RL writers...)
The
2E Domains of Dread is the resource to go for if you play 2E, though the Black Box is of course mandatory. Domains of Dread first introduced native characters, special Ravenloft classes and races rules. It is a bit pricey these days though.
If you're on a budget I'd recommend getting cheap Ravenloft lots from ebay, and/or relying on netbooks articles or free adventures from the sites above. And check out the marketplace thread on the FoS General forum for great advice on where and how to get stuff cheap.
Night of the Walking Dead is available as a free download here:
http://www.wizards.com/dnd/files/notwd.pdf It is a classic introductory RL adventure set in the domain
Souragne, a fantasy pastiche of Lousiana. The FoS have made a 3E netbook for this domain available in their downloads section. This domain was only scarcely described in the canon material, so basing your campaign in a domain like this will help you keep your budget low, but you'll also have to improvise and rely on netbooks and articles.
Another great resource for cheap and great 2E adventures written or adaptable for RL is Dungeon Magazine. The FoS has a list of all Ravenloft Dungeon adventures, but there are many more which are easily adaptable to RL. Check out
this Dungeon index or
this one