In Joomla 1.0.x we can add new module positions by going to

Site -> Template manager -> module positions (total 50 places). [Add your position]

However in Joomla 1.5.x we need to add the module positions within the templatedetails.xml under the active template folder

<positions>
<position>hornav</position>
<position>breadcrumbs</position>
<position>banner</position>
<position>left</position>
<position>right</position>
<position>top</position>
<position>search</position>
<position>topsl</position>
<position>user1</position>
<position>user2</position>
<position>user3</position>
<position>user4</position>
<position>user5</position>
<position>user6</position>
<position>user7</position>
<position>user8</position>
<position>user9</position>
<position>footer</position>
<position>syndicate</position>
<position>debug</position>
</positions>
Simply add another line(s) with <position>your module position</position> and place it in the order it will appear within the list