You can in your forum admin under vbGallery -> Manage Addons alter the stuff displayed on the forum.
There is no usergroup permission that I know of that says a group can or can not post links. That must be some default vb
hard coded things as I already noted to you you can type out the url just do not put http:// its is easy enough to do.
You should be able to upload attachments so you could post an image also.
I am not sure what spacing your talking about but no doubt your probally talking about custom editing some template or style to achieve the look you want.