you can create your own page templates. you can put your form stuff on these custom page templates. I might use one page template, and use some php to tell if there are post values. (use post instead of get, so you don’t conflict with wordpress). Process the post values if true, or write the form if false. So the first time a person comes to the page, they see the form. They enter values, hit submit, and the form takes them to the same page. But this time there are post values, so you instead do whatever it is you want to do with them.
http://codex.wordpress.org/Pages#Creating_your_own_Page_Templates
