Hi Mike,
I can't give you a full solution, but you may be getting an error due to the use of $HTTP_GET_VARS.
Try using $_POST, or if you are running php version prior to 4.1.0, use $HTTP_POST_VARS. (Note that the form contains post variables in your code).
You can find out more on global variables in php here:
http://uk2.php.net/reserved.variables
Otherwise, the only other potential issue I can see is the variable $form. This is undefined, but I imagine that is more to do with the fact that it is defined in another snippet of code.
Good luck!
Sanj