How to POST and PARSE HTTP Data in Objective C

I have written Windows/PocketPC based applications to communicate with various payment gateways.  And am now looking to provide same for the iPhone.

The only trouble I am having is with the POST to the gateway.  In .Net we use something like this:
HttpWebRequest objRequest = (HttpWebRequest)WebRequest.Create(post_url);
            objRequest.Method = "POST";
            objRequest.ContentLength = post_string.Length;
            objRequest.ContentType = "application/x-www-form-urlencoded";

            // post data is sent as a stream
            StreamWriter myWriter  = null;
            myWriter = new StreamWriter(objRequest.GetRequestStream());
            myWriter.Write(post_string);
            myWriter.Close();

            // returned values are returned as a stream, then read into a string
            String post_response;
            HttpWebResponse objResponse = (HttpWebResponse)objRequest.GetResponse();
            using (StreamReader responseStream = new StreamReader(objResponse.GetResponseStream()) )
            {
                post_response = responseStream.ReadToEnd();
                responseStream.Close();
            }

I am using the code below and the returned data is HTML not the data expected.  In .Net you form the request and then create a StreamReader to grab the data.  Am I missing a property from the NSHTTPURLResponse??  Or am I going about the wrong way??

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-(void) createRequest 
{
	NSLog(@"Made it to createRequest");
	NSData *postData= [myString dataUsingEncoding: NSASCIIStringEncoding];
	NSString *postLength=[NSString stringWithFormat: @"%d",[postData length]];
	NSError *error;
	NSHTTPURLResponse *response;
	
	vmURL= [NSURL URLWithString:@"https://www.gateway.com/ProcessCard.do" ];
	vmRequest=[NSMutableURLRequest requestWithURL:vmURL];
	[vmRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
	[vmRequest setValue:postLength forHTTPHeaderField:@"Content-Length"];
	
	[vmRequest setHTTPMethod:@"POST"];
	NSLog(@"create   %@:%@",[myString class],[myString dataUsingEncoding: NSASCIIStringEncoding]);
	[vmRequest setHTTPBody: postData];
	
	NSData * data = [NSURLConnection sendSynchronousRequest:vmRequest returningResponse: &response error: &error];  
	NSLog(@"\n \n%@",data);
	NSMutableString *str;
	str=[[NSString alloc] initWithData: data encoding: NSASCIIStringEncoding];
	NSLog(@"\n \n \n %@",str);
}