How to insert data to MySQL having auto incremented primary key?

The default keyword works for me:

mysql> insert into user_table (user_id, ip, partial_ip, source, user_edit_date, username) values 
(default, '39.48.49.126', null, 'user signup page', now(), 'newUser');
---
Query OK, 1 row affected (0.00 sec)

I'm running mysql --version 5.1.66:

mysql  Ver 14.14 Distrib **5.1.66**, for debian-linux-gnu (x86_64) using readline 6.1

In order to take advantage of the auto-incrementing capability of the column, do not supply a value for that column when inserting rows. The database will supply a value for you.

INSERT INTO test.authors (
   instance_id,host_object_id,check_type,is_raw_check,
   current_check_attempt,max_check_attempts,state,state_type,
   start_time,start_time_usec,end_time,end_time_usec,command_object_id,
   command_args,command_line,timeout,early_timeout,execution_time,
   latency,return_code,output,long_output,perfdata
) VALUES (
   '1','67','0','0','1','10','0','1','2012-01-03 12:50:49','108929',
   '2012-01-03 12:50:59','198963','21','',
   '/usr/local/nagios/libexec/check_ping  5','30','0','4.04159',
   '0.102','1','PING WARNING -DUPLICATES FOUND! Packet loss = 0%, RTA = 2.86 ms',
   '','rta=2.860000m=0%;80;100;0'
);

Set the auto increment field to NULL or 0 if you want it to be auto magically assigned...