I would suggest you refrain from going to the big track (especially Sears) until you learn a bit more about the handling dynamics of your car.
You are up in Rhonert Park so you should look into the RedWood Region PCA
find information here...
http://red.pca.org/
look under autocross for information on their series.
They do most of their Autocrosses at Shultz airport.
Newbies are always welcome, instructors are always available...check it out.
Do not under any circumstances go out with a non-Porsche centric group until you have the basics.
Why not be instructed by folks that drive the same cars and know their strong and weak points?
there are quite a few folks on this board that are into AXing and tracking their Boxsters...
I ran my '99 on track and AX for 5 years...they are great at both...you just need to learn the basics.
here is a shot of myself playing tag with my good buddy in his Euro Carrera clone with a 2.7RS motor in it. The two cars were very equal overall at Buttonwillow. This was several years ago, we have both moved on to 964s since then.