I have a 2008 tacoma with 19000 miles and the check engine light gives a code for a small emissions leak? Should I worry about this if my truck runs good? what could be the cause? is this covered by warranty? and is it common? should i just reset it and see if it comes back on?

You only need worry about the CEL (Check Engine Lamp) if you live in an area that has Enhanced Emissions Testing (like California).
I would guess that the code that caused your CEL to come on refers to a leak in the Evaporative Emissions System (EVAP).
At the age of your vehicle and it's mileage, it is indeed covered under both the basic and Emissions warranties. Be aware that it is standard dealer procedure to require your authorization for inspection and diagnosis of the problem. Usually 1 hour of labor. If the service department determines that the problem is covered by your warranty, then you should be no charged.