When your web browser submits a form, what it's doing is posting the values for the fields in this format:
"name1=value1&name2=value2", so in this case "user_id=whatever&password=whatever".
You'll need to gather where the form is submitted (it's in the HTML source code, usually called the "action" or something like that), then you need to post the data yourself.
A very simple example of this would be something like:
Code:
NSString * postString = [NSString stringWithFormat: @"user_id=%@&password=%@",theUserName,thePassword];
NSData *myRequestData = [NSData dataWithBytes:[postString UTF8String] length:[postString length]];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString: @"http://www.theaddress.com"]];
[request setHTTPMethod:@"POST"];
[request setHTTPBody:myRequestData];
NSData * response = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
[request release];
Hope that helps!