mtcarey,
Any plane that will allow you to fly in a straight and level line, do a roll and a loop is a good plane to start flying pattern with. It does not have to be per say, "a pattern plane", they just look cool.
I would reccomend that you go to the NSRCA website and download the current Sportsman pattern if you haven't already, and just fly the maneuvers that are listed with your current airplane. If you have a local pattern flyer ask him to take time to go through the schedule and explain to you what the judges will be looking for meaning centering, presentation, etc. (If you don't have a pattern flyer locally that can offer you some help, give me a call and I will help you) If the plane that you are currently flying will allow you to fly through the Sportsman schedule begin to practice that schedule and go to a contest as soon as you can.
From what I have seen at past contests I don't think that you will be dissappointed with the results of alot of practice. After attending your first contest I believe that you will leave knowing a couple of things, the main thing being if you even want to persue pattern the second being alot better understanding of why the more current designed pattern planes look the way they do. Keep in mind that Sportsman is an introductory class and that noone is expecting you to show up with a full blown pattern ship.
You will most likely recieve alot of input to your question and this is only my opinion
Russell Honea
www.patternproz.com