I am trying to write a export script for blitzbasic .b3d file format (www.blitzbasic.com) and there file format does not support quads.

Is there a way (or script) already to triangulate a given face?. Failing that, im after a inteligent way to convert a given quad face to two triangles.

if len(face.v)>3:
#need to triangulate
else:
#its cool!

(just incase you was wondering what i was on about

As far as I know, work was started with the new python API (225) to triangulate any ngon mesh, but I donβt think it made it to the actual release version. In any case, triangulating a quad is very easy, you just have to make sure you connect vertices in the right order to preserve the face normal. Which for a blender quad with vertex indices (0,1,2,3) would be (0,1,2) for triangle 1 and (2,3,0) for triangle 2.
Just in case you need a code example:

import Blender
ob = Blender.Object.Get(meshname)
me = ob.data
nme = Blender.NMesh.GetRaw()
for v in me.verts:
nv = Blender.NMesh.Vert(v.co[0], v.co[1], v.co[2])
nme.verts.append(nv)
# creates new all-triangle mesh
# ignores single vertices and edges
for f in me.faces:
# number of vertices used for this face
numv = len(f.v)
# if triangle, copy as is, else, if quad, create two triangles
if numv==3:
nf = Blender.NMesh.Face()
nf.v.append(nme.verts[f.v[0].index])
nf.v.append(nme.verts[f.v[1].index])
nf.v.append(nme.verts[f.v[2].index])
nme.faces.append(nf)
elif numv==4:
nf = Blender.NMesh.Face()
nf.v.append(nme.verts[f.v[0].index])
nf.v.append(nme.verts[f.v[1].index])
nf.v.append(nme.verts[f.v[2].index])
nme.faces.append(nf)
nf = Blender.NMesh.Face()
nf.v.append(nme.verts[f.v[2].index])
nf.v.append(nme.verts[f.v[3].index])
nf.v.append(nme.verts[f.v[0].index])
nme.faces.append(nf)
Blender.NMesh.PutRaw(nme, "TRIMESH")
Blender.Window.RedrawAll()

Which creates a triangulated mesh from whatever mesh you gave as argument (ignores rotation,location & scaling)