Not sure where you got the idea that you can convert a burner to read a DVD from, althogh they look very similar, the harware and software in both have nothing in common.
The Ricoh burners (and I'm sure others) that can read DVD have both sets of hardware in the unit to allow that and priced accordingly.
With the price of DVD players is now so darn cheap (as low as $80 in Australia), I really cant see any reason to convert, even if it was possible.