Just bought Left4Dead on steam,
username is
Conscept
Welcome
Here are my tips on getting startied with L4D.
1. Install the game

2. Get a mic
3. Play some campaigns on easy/normal/advanced/expert until you get used to the weapons and general way to get around and what to avoid (tanks/witches)
4. Add some of us to your friends list (there's a L4D Steam Names thread somewhere)
5. Join in the L4D Versus fun!
Most people on here welcome new players so long as they have an open mind, don't mind getting tips on where to stand, what to do in certain situations etc, don't rage - it's only a game! Don't go out of your way to grief other players and generally be friendly to your fellow players.
Games generally start from 7pm onwards, I normally get a quick game during the week (I'm Defrag - people generally know who I am and to avoid

) around this time and finish about 8:30, I know other players are on it longer than that though. Weekends tend to be a free for all and you can get a game any time of the day (or night).
There are lots of regular players that are very good, so don't be discouraged to find you get killed a lot during your initial vs games, we'll try to take it easy and it can be a tough learning curve especially as most of us have had the game for a while now.
Some names to watch out for online (in a good way)
Link to Insanity
Bledd
Kearney
Sh4rk
Dingleberry
Lagmeister
Defrag (me!)
Pod
Forgetful Fish
Ghurka/Pimp
Qlimax
.... the list goes on. Joining a game with these people pretty much guarantees some good friendly fun.
Oh, and above all - have fun.