Just my opinion, but if you find the drum questionable you probably won't be tremendously impressed by the disc, either. I consider them pretty much apples-for-apples.
That said, in terms of parts you'll need the following:
Left lower fork leg (rights are all the same, earlier is better cuz it some still had drain plugs)
Front wheel w/disc.
Master cylinder and brake hose.
Starter/kill switch from post-'01 TW (optional). If you use your existing switches the starter button will be pointing toward the ground due to the master cylinder and throttle cable locations. More of an inconvenience than it is a complete nuisance, but worth doing.
You'll need to splice the plugs from your early model brake switch onto the master cylinder brake switch because the later switches are a larger diameter.