Two step process:
Step one: sell the MTB.
Step two: buy a good road bike.
There are intermediate steps you can take, but ultimately, you can't get there from a MTB. If you want a little better performance, then by all means install narrow slicks, and trekking handlebars. Installing racing style drop bars will trigger a lot of relatively expensive changes: new shifters, new brake levers, etc. At that point, N+1 (just add a racing/road bike to the fleet), or sell what you have and pick up what you want.
Many of us got back into riding on a MTB. I know I started back riding three years ago on a Trek 800 MTB. It has long since moved on to another home.
I now have a larger fleet, and I do still have a MTB set up for trail riding: its a Trek 950 with butterfly bars (similar to trekking bars, but a little different).
Here it is with 26 - 1.25 slicks.
