Hi dudleyfire,
Port forwarding in Juniper SRX is destination NAT, there is this Juniper Day One Series book you'll probably enjoy called "Day One: Configruing SRX Series with J-Web" :
In it you will find a chapter on how to configure NAT ( including destination NAT ) using the J-WEB on page 58. Though the example is only for source NAT destination NAT is basically the opposite.