threaded to threadless conversion will require:

new headset,
new forks,
stem
star fangeled (sp?) nut

you are going to have to remove the old headset from the head tube, then replace it with the new headset, your lbs can do it with a press or if you are careful you can do it with a c clamp and two pieces of wood. then put the fork in and attach the stem, and see where you want to cut the steerer tube on the fork.

it's not too terribly difficult