If you are developing a new joomla 1.5 template or are editing any pre existing one, and need to add a new custom module position of your choice some where in the template index.php, here it is how to do it (you will be able to select this new module position from the Joomla! 1.5 admin backend for modules to be published at this new position):
1. Goto <joomla root>/templates/<template name>/ folder
2. Open the file index.php in that folder in your favourite editor
3. Add this code in the relative position in html of the template index.php to add the new custom module position in your Joomla 1.5 template
<?php if ($this->countModules('custom')) : ?>
<div>
<jdoc:include type="modules" name="custom" style="xhtml" />
</div>
<?php endif; ?>4. Rename the word custom coming twice in the above code with any name that you want to give to that new module position.
5. Open templateDetails.xml in the same folder and find the part of code where it says <position>
6. After the already existing positions, simply add the new position that you just created in the above step in your Joomla! 1.5 index.php in the same format as the already existing ones.
<position>custom</position>
7. Replace the word custom with the name of the position that you defined in step 4 above while adding the new module position code for Joomla! 1.5 in template index.php file.
This will add a new custom module position in your Joomla! 1.5 template which you can use to publish modules at this new position. You can repeat the same procedure for more custom module positions for Joomla! 1.5 template.