Process form in separate php file

Hey everyone,
I can’t get a php page to work. I have a form that submits using post, a file and some fields. The php page that handled the input is in the form of a template in the theme folder.

The problem is that while I can make the page spit back $_POST information, I’m not able to get ‘get_header()’ to work. I’m also unable to get ‘$wpdb’ to work.

Do I need to include something in the php page for this to work? I need to use a seperate php page since I’m uploading a file and so can’t use javascript. the form is a part of a plugin I’m writing.

Thanks,
ravster