Most softphones use port 5060 by default for SIP. The process for registering a softphone should should be very simliar to registering a hard phone:
http://www.ringroost.com/how-to-set-up-and-register-a-sip-phone.php#step_4_1
Some softphone will have both a Auth Name & Username, ensure your enter the "SIP User" provided in both those fields.