Joomla 1.5 has come a long way since Joomla 1.2. Earlier if you had to customize a module you had two choices:
1. Edit code in the actual module file.
2. Write custom code to implement the functionality.
Choosing either of the two steps would involve more time and in the end it also invited the chance of more bugs into the working of the system. However, with the advent of Joomla 1.5 you don’t need to go through all that hassle.
You have to navigate to the module folder in which you have to make the customization and make the changes in the files present in the tmpl folder. This has considerably improved customizing functionality according to requirements. Now, the developer does not need to have to do anything in the actual code file of the module rather he just has to use the methods exposed to him in the tmpl folder and customize them.
Try Joomla 1.5 today and you will definitely see the difference.