I use a bounding box test first, and if it's in that I run another test based on the following :
http://www.geometryalgorithms.com/Archive/algorithm_0103/algorithm_0103.htm
which looks like the same method that Indiepath posted.
http://www.geometryalgorithms.com/Archive/algorithm_0103/algorithm_0103.htm
which looks like the same method that Indiepath posted.