how to use drupal_http_request

I'm currently developing a module that integrates dimdim and drupal 6.

I am having some problems formulating the http post request to create a new instance of a conference room.

I have sighted the API for drupal_http_request but since this is my frist time working with it am not sure if I am using it correctly. If anyone has any suggestions that'd be great. Here's the code I'm using to try to call it:

	//issue http_request
	$headers = array();
	$dimdimserver = variable_get('dimdim_server_location', 1);
	$dimdimport = variable_get('dimdim_server_location_port', 1);
	$url = $dimdimserver . ':' . $dimdimport . '/portal/start.action?';
	$headers['name'] = variable_get('dimdim_name', 1);
	//$headers['email'] = variable_get('dimdim_email', 1);
	$headers['password'] = variable_get('dimdim_password', 1);
	$headers['returnurl'] = variable_get('dimdim_return_url', 1);
	$headers['waitingarea'] = 'true';
	$headers['startDate'] = $textdatestring;
	$headers['meetingRecurrance'] = 'SINGLE_EVENT';
	$headers['startHour'] = $hournozero;
	$headers['startMinute'] = $minutesnozero;
	$headers['timeAMPM'] = $ampm;
	$headers['displayname'] = $node->host;
	$headers['hours'] = $node->hours;
	$headers['minutes'] = $node->minutes;
	$headers['confname'] = $node->title;
	$method = 'POST';
	drupal_http_request($url, $headers, $method, 0, 3);

Is there any way of testing what's actually being called in the full url with the headers tacked on the end? I tried to do a drupal_set_message but it didn't like it.