The type of knob you have has 2 sets screws. Loosen them both and after a little wiggle to dislodge 20 years of sweat and dust, it should slip right off. You don't have to take them out all the way, but if you loose one, replace with 6/32 x 3/16 set screws from a hardware store.
You'll need a 1/16 hex driver for the set screws.
When you replace the knobs, to make sure they aren't riding on the top of the finish, put a business card on either side of the nut holding the bushing before tightening, then check to see if you've got the knob on straight.
The other knobs you've heard about are held on by a collet. It's easy to loosen if you take the cap off the knob. If you don't loosen those, when you take the knob off, the shaft of the pot will come off at the same time.
[Thanks, Edwin! I started this message, went out the shop for a second]
(Message edited by mica on November 01, 2005)