Hi, sboro -
How do I post a message on the message board...
You just did!
If you mean in the place where you would like it to be, specifically to start a new Topic of your own -
In Discussions, new Topics can be created only when viewing a Forum page; they can not be created when viewing a Category page.
A Category page would be one like this -
http://discussions.apple.com/category.jspa?categoryID=99
Note that the word 'category' is the last word in the URL before the 'ID=###' element of the URL. The word 'Category' is also displayed as part of the pagename for the above page; that page element is immediately below "Apple Discussions" in the upper left of the page.
In order to post a new Topic within a category, you would need to enter one of the forums (in this case one of the two forums) shown in the upper section(s) of the page. In the example, and for this thread, you would enter the "Using Mac OS 9.x" forum -
http://discussions.apple.com/forum.jspa?forumID=669
Note that the URL for that page has 'forum' as the last word preceding the 'ID=###' element, and that the pagename includes the word 'Forum'. Once you are viewing a forum page, there will be a new link in the upper left, under the pagename: "Post New Topic". Click that to create a new Topic of your own in that forum.
***
...what does the dot in dot com stand for?
Don't know exactly, other than the word 'dot' is used to verbalize the period that precedes the element "com" in an internet address, such as Apple.com (pronounced aloud as "Apple dot com"). The convention of pronouncing the period as "dot" is also used for other domains, such as Fred.org (Fred dot org), etc.
The word 'dot' is also often used in text work to represent the period in URLs.
For one reason, it's easier to see or refer to "dot" than it is to see or refer to ".".
Another reason is to foil bots sent out to harvest email addresses - such as by using "meATplaceDOTcom" instead of "me@place.com".
Yet another reason is that most of us seem to think in those terms. When I'm typing Apple.com, I spell it out for my fingers as "capA p p l e dot c o m" rather than "capA p p l e period c o m".
As for the function of a 'dot' in a URL - don't know the technical lingo, but it is used as a separater, a specific character used to separate different elements of an address. This allows the processing computers at the central server farms to identify an address and direct traffic to where it should go.