I have a level 20 resto pally, and though I've played WoW for 6 years this was my first time tanking...

I came in 4th out of 5 players in dps in Shadowfang Keep (beat out the healer lol). Is that normal for a tank, or should I also be doing more dps?

Also, are there any plug-ins out there that will help me as a tank?
Sorry, that should say Retribution pally, lol...

Protection is the tanking spec. though....
if you aren't using Protection (spec) then you have to use that because Retribution is for DPS and resto is healing. but it is completely normal for tanks to have low DPS, unless of course they are extreme BoA.