Hallo, I searched for Intersect (in Blender 2.54 MathUtils) , not found?
Intersect finds (or not!) an intersection point of a ray (point and direction) in a plane defined by three vertices

After some symbolic computations I found out that cross and dot products do the job!

If not, I would suggest to supplement mathutils with something like my version
(extra eps parameter for numerical problems, what should be considered zero [absolute value]?!)