How can we theme menu blocks in drupal 6 I decide to theme menu blocks in my drupal 6.x.

I have copied block.tpl.php into my theme folder and I have renamed it to block-menu.tpl.php

but it seems it doesn't work !!

How can I modify the theme for menu blocks?
You can user the theme developer module to check whether your template is called at all. It will show you what nameing conventions to use.

And just in case: You have to flush your caches to make sure new templates and theming methods are taken into account.