Jerry,
        Here are a bunch of my favorite links.
I think the first answers your question.

Karl Bates

http://www.geocities.com/CapeCanaveral/Lab/9643/TraceWidth.htm

http://www.automata.com/engtools/enghome.htm

http://www.aracnet.com/~dynacad/download.html

http://www.aracnet.com/~gpatrick/pcb.html

http://highspeeddigitaldesign.com

http://softwareshop.edtn.com/netsim/si/termination/

http://softwareshop.edtn.com/netsim/si/crosstalk/

http://www.polar.co.uk/

http://www.ultracad.com/articles.htm