how do you make cat ears and a tail to go along with it for anime cons?

Answer 1

This site has directions for making cat ears. It's for cat and mouse ears.
http://sewing.about.com/library/weekly/aa092100e.htm

This site has the directions for making a whole cat costume, but it does explain how to make a cat tail.
http://members.aol.com/pumpkinave/costumes/catgirl.htm

Answer 2

A tail is fairly easy. Just get the cloth you want and cut a long, narrow stip. Fold it in half so the material you want showing is then sew the long side and across one end so you have a tube. Flip this tube inside out (this is the hard part, be patient) then you can either stuff it or leave it empty depending on how firm you want it to be. Some people put thin, flexible wires in their tails to give it a curve. As for the ears, I'm not so sure. I just went out and bought some in the Halloween section of a store because I couldn't find any good patterns. Good luck!