Milton

I do not know the trick or preferred way since I have no image options either but.....if you put something up on photobucket or a similiar image hosting site you can post a pic here in the forum by using image tags like this:

[img]your http link to your photo[/img]

notice the brackets and the added slash on the last img tag....that will make your photo appear on the forum.  I am pretty sure that you can only use jpeg, gif, or png type files.  CAD file types will have to be converted to an image format first.

hope that helps you
TOmmy

This is from the help section of the forum under frequently asked questions.
How do I attach images and other files to posts?
If attachments are enabled in the forum and the specific board you want to post in, first submit your post without the attachment, after that you can click the post's Attach button to go to the upload page. Posting and uploading is separated this way because uploads can fail for various reasons, and you probably don't want to lose your post text when that happens.