I'm no optical scientist, but seeing as the diffraction grating being used is recycled from a DVD and the sensor is a consumer webcam, I wonder how accurate/reproducible the results would be.
Gratings like this (or a CD) will work, but they introduce plenty of artifacts. Scratches and material nonuniformities can scatter light in a way you don't want, and reduce the (already limited) amount of light hitting the right spot on the sensor.
A conventional diffraction grating is pretty inexpensive ($2.50): http://www.rainbowsymphonystore.com/difgratfilsh.html