For those of you, like me, who had no option to send or receive private messages... I have figured it out!
You can access these forums EITHER originating from theknot.com OR weddingchannel.com. If you come from the wedding channel... no private messaging! Just go to theknot.com and go to the forums from there... same forums, but now you have PMs. (Though I kinda prefer the purple weddingchannel color scheme hehe)