What are you looking to gain? Speed? More hand positions?

As an observation, you would pick up some of the benefits of a drop bar bike by raising your saddle, if speed is your objective...this would allow you to do 3 things.

1) Ride in a more aerodynamic position.
2) Extend your legs for better efficiency.
3) Cost nothing.

This could be done in conjunction with trekking bars previously mentioned.

While I have seen some bikes that people have converted, unless you have a lot of the components on hand, because the bicycle manufacturers get great prices on components, it may cost as much as buying a similar quality drop bar bike. Clifford pointed out how come the process can get more expensive than you would initially think. It gets really expensive if you want the modern integrated drop bar brake/shift levers.

Also, I would be hesitant to convert a bicycle with front suspension into a drop bar bike... No concrete reason, it just strikes me as something I wouldn't want to try personally. It may be fine.