where can I find out how to? I understand rack and pinion but want to
use another method.

What exactly do you want to do with it? Will you be
moving in just one direction or will it be a
reciprocating motion? One of the most common rotary to
linear motions is the scotch link. It uses a rotary
crank pin inside of a sliding block which rides in a
slotted link. It works fine but depending on rpm it
has great(poor)friction and wear properties. There is
also the common crankshaft with a pitman arm riding in
a set of guides.
gbritnell

If you're talking moving a sternwheel with realistic moving pitmans,
I have photos and a diagram for the one I built for mine at...
http://www.dragg.net/jbrown/construc2.htm