Hi Adam,
"and what tool/interface I need for this" : any particular interface or tool. Just the PHP page where you receive your form datas + a PHP page where you'll write all methods(functions) you need (and you must have NuSOAP library too, of course ^^).
So, in the first PHP page with your form datas :
 	
	<?php
 
   //the following require_once() path must be a relative path
 
   require_once('../path/to/nusoap.php');
 
   //the nusoap_client() must be an absolute URL
 
   $nusoap = new nusoap_client("http://www.website.com/my_methods_page.php");
 
               
 
   //here you make your datas array
 
   $datas = array(
 
      'name' => 'Bubu',
 
      'job' => 'developper',
 
      ...
 
   );
 
      
 
   //Now, you call the method "registerUser" (in my_methods_page.php) by passing your datas array we'll just print_r()
 
   print_r( $nusoap->call('registerUser',array( 'datas' => $datas )) );
 
?> | 	
 
Now, in my_methods_page.php :[/u]
 	
	<?php
 
   //the following require_once() path must be a relative path
 
   require_once('../path/to/nusoap.php');
 
   
 
   //instanciate a new soap server
 
   $server = new soap_server();
 
   
 
   //declare all your existing methods (note that only methods called somewhere else than here must be declare. no need to declare privates)
 
   $server -> register('registerUser');
 
      
 
   //your method to register
 
   function registerUser($datas)
 
   { 
 
      //here your code to write in database. i just wrote a return for you to see the print_r() result : your sent datas array.
 
      return $datas;
 
    }
 
   
 
   $HTTP_RAW_POST_DATA = isset($HTTP_RAW_POST_DATA) ? $HTTP_RAW_POST_DATA : '';
 
   // Executes the RPC
 
   $server -> service($HTTP_RAW_POST_DATA);
 
   
 
?> | 	
 
i hope it will help you (and hope i don't forget anything 

)
BenoƮt
PS : sorry for my english