It's a shame no one answered your post on here. I started with a 29 gallon saltwater aquarium myself back in 2004, then upgraded to a 75 in 2006.
As of March 2007 (looks a lot worse now
):
Here are some good message boards where you can ask specific questions and gain some general knowledge:
1) My personal favorite,
www.myfishtank.net. I post under the name of dbacksrat but haven't been online for awhile. You get lots of personalized attention over there. Also there are not a lot of flaming lib tards and quite a few are retired military.
2) This site has a lot of great information if you ever want to set up a reef tank:
www.reefcentral.com. However, it is very impersonal and full of liberal idiots. I have been banned from there a few times and have since handed my account over to a buddy.
Anyway, back to your tank. A 20L is perfect for starting out with saltwater. Most of your freshwater equipment will be compatible with saltwater too. You would probably want to pick up a powerhead, a protein skimmer, and about 20 lbs of live rock.
As far as fish go, an ocellaris clownfish is fine, that was my first fish in 2004 (I still have him). I would advise against the anemone for now because they are difficult to care for and need intense lighting, perfect water, particular water flow, etc.
Other fish you could have are gobies, blennies, damsels, cardinals, grammas/basslets, etc. A great site for browsing and looking at possible fishes:
www.liveaquaria.com.
If you have any further questions feel free to ask.
You'll find that saltwater tanks can be just as bad as an addiction as ARs.