Default values for "Post New Topic"

I'm trying to set up a link externally in my site so that when some one clicks on it they are thrown to the "Post New Topic" window and there are a couple of defaults thrown in.

I can get the subject by filling in strTopicSubject and altering a little code but what do I have to set and where would the code be if I wanted to place default values in the Message body? I'm actually going to throw in a dynamic image tag but that's neither here nor there really is it.

Thanks in advane to all the people out there smarter than me.