That's a nice bike. 27-speed Shimano Deore shifting, Hayes brakes, Manitou fork. (Bikepedia link). Compared to the average commuter bike, yours is already better.

Get some lights. Slicks are an easy win.

I wouldn't swap the fork. For road use just dial up the damping and preload.

You might find that nicer MTB wheels are now going to bigger axles. What you have is probably fine.

In order to upgrade your shifting you are looking at a complete drivetrain swap. When Shimano went 10-speed with their mountain groups, they changed the rear cable pull, narrowed the chain and cogs, narrowed the cassette spacing, and nothing is compatible any more. Fortunately it's not an insanely expensive upgrade if you get the parts from the British gray market (like this $187 for Deore). And the new stuff is pretty nice.

Between the added efficiency and smaller diameter of the slicks, and the lower bottom cogs on the 10-speed, it's nice to have a higher crankset. I put a 26-36-48 crankset on my bike and it does better on the road than it did with 22-32-42. Same derailleur works for both, you just need to scoot it up.

You might have trouble with racks and fenders due to the disk brakes. You may lack the mounting points that are usually at the brake bridge, you might lack eyelets at the fork ends and dropouts, and even if you have them, the calipers might interfere.