Must it be SNMP traps?
IOS writes to syslog when someone enters the config mode (but doesn't necessarily mean the person makes a config change):
*Mar 1 17:56:48.596: %SYS-5-CONFIG_I: Configured from console by Cisco on vty0 (10.0.0.42)
That simply takes
! logging to the circular "show log" buffer, at level 5--notification
logging buffered [buffer size] notification
! logging to remote syslog server, at level 5--notification
logging trap notification
logging source-interface [interface of choice]
logging
If you truly want to receive SNMP traps for those syslogs, you could add the global config:
snmp-server enable traps syslog
However, it's not really a good practice.
In more recent IOS releases, you could do fancier config change tracking, as outlined in this article:
http://www.nil.com/ipcorner/RouterConfigMgmt/
