I'm certainly not an expert (I've only done it twice) but I've had good luck doing it myself.
The first time I used model enamel and a ruling pen. Worked ok, though the line is a little thin. I just laid a steel rule on the tubes as a guide. The ends I freehanded. For the lugs just follow the contour. For gold I've used the thin metallic pens from the stationary store, actually seem to dry pretty hard, though I wouldn't want to scrub it with solvent.
For my second attempt (see my Legnano on CR) I bought one of those wheeled liners at the car show. (I'd have to find it to get the name). They work pretty well, but take a little practice. I just used the edge of the tube as a guide holding my hand position firm as I drew down the tube, like someone with a striping brush would do.
I definitely recommend the One Shot sign enamels: they're very finely ground and smooth.
I did buy a Flow Pen on Brian B's suggestion but haven't tried it yet.
All said, if you could master a striping brush it would probably be the best for the lining, though I know Harley does their tanks with the wheeled thingie.
To anyone I'd say give it a try, its not that hard and even slightly rough results look pretty good. With the enamel over Imron, its easy to wipe it off if you goof with mineral spirits.
If I had time, I'd love to airbrush and stripe the old Allegro frames I have kicking around.
Ted Williams
Too many interests in Oakland