Not very well. You need a decent vector based app to do that and photoshop 6's vector funtions are pretty ropey to say the least. The best you can get is to use the freeform pen tool, and set the curve fit to 10 (I think this is the highest setting). It works ok for long, sweeping lines, but sharper curves tend to turn angular. You'll then have to stroke the paths with a brush, but if you're going to do this I'd seriously recommend upgrading to photoshop 7 as the brush system has been totally updated, and is really powerful.

You could use illustrator (or something similar) and import the drawing into photoshop if you need to, or alternatively use flash (Which has really useful animation features), but this may not be practical for whatever you're doing.