Forum posting is place where you can discuss anything about any topic and you can create thread by their own.Owner of that forum posting site just have to control the activity of the users. But in Blog posting is place where the owner of that website place various blogs which provide information of any product and services and the users can read it and place comment on that particular blog.but here discussion is not possible.
I would like to say only in one line: Blog - Online dairy (Where you can write your daily activities, about you etc..) Forum - Only for share knowledge, techniques and discuss with others.
A man told his doctor he wasn't able to do all the things around the house like he used to. When the examination was complete, he said "Now Doc, tell me in plain English what is wrong with me." "Well in plain English," the doctor replied, "you're just lazy." "Okay," said the man. "Now give me the medical term so I can tell my wife." From 24discountgolf
i believe it the same. No matter forum or blog , is a place to share your problem, solution and opinion base on the topic. What different is how to get it link back , Forum is get backlink through signature while blog is get backlink through a link back from clicking your name.  Â
Blog posting differentiates from forum posting in that blog posting you leave your site in a url field while in forum posting you usually have your site in your signature
Blogs and Forums are very important to get back links and it is helpful to get traffic and high PR to your site. Blog commenting and Forum posting are free techniques to promote your business.