This could be a comment but. . . 

In all seriousness, probably the best help anyone can give you is ["read the manual."](http://cran.r-project.org/web/packages/rpart/vignettes/longintro.pdf)  Since we don't have access to your data, I am guessing that pages 39- 40 of the manual will help you.  

Also I could point you to the `rattle` package: this is a pretty simple point and click interface to the `rpart` package, along with several other modeling tools.  

By the way: as noted on the 2nd page of the manual, CART is a trademarked name.  "Recursive Partitioning" is a generic name, so you should probably describe your model accordingly.

I hope this helps.