4
Administration Menu -> System Admin -> Blocks
Scroll to the bottom and fill out the form with which pages it should be visible on and where on the page it should be.
Put text in the textarea using standard tags such as [img] and [url] (you have shortcuts to the tags by using the icons above the input textarea)
Set "Content Type" to "Auto Format" and press submit
Now all you need to do is go to Administration Menu -> System Admin -> Groups and edit the various groups who should be able to see the block and set their "block access rights" to include this new block.
