Cast your ray, determine which coordinate is the point of contact(if result is global you will need to calculate local coordinates in relation to the object being ray cast upon ie calculate the difference)
Grab a mesh of your object
Convert your objects mesh into memblock data.
Every 3 vertices is 1 triangle/polygon in the memblock - these are all local coordinates, hence why step one needs anything global converting. So you can then iterate through each poly/tri in memblock and compare the ray cast coordinates to each of the tri/poly's vertices by calculating distance. The smallest distance is the poly/tri where the ray cast contact point occurred. Use the position within the memblock as a reference to which poly/tri is being targeted.
The above points seem simple, however if you are unfamiliar with memblocks you need to get stuck into them first as you will presumably be wanting to create a visual representation of the tri you are aiming at which will then involve creating your own object to overlay at the exact position required. Memblocks are relatively easy though so you shouldn't have too much of a problem
Win 7 Pro 64 bit SP1, AMD A4-5300 APU 3.4GHz, 8GB DDR3, NVidia GeForce GTX 750 1GB GDDR5, ASUS A55BM-E
