How to add vertical hover navigation sub-menu?

hi all,
I have an horizontal menu,but the menu items all are in image format.when mouseover on it, it display another color means it is in active state.(this is also an image of another color to differentiate active or not).

Now i want to add vertical sub-menu of diff levels to the already existed menu(i.e original menu is of image format). Is it possible to add the sub-menu items to the image menu? if possible, i want the solution for it.

Format :::

Home(image format) Example(image format) Download(image format)
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Ex on php
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Ex on MySql
The sub-menu items will display only mouse over on the main menu…

Thanking you…

Expanding menu’s is more of a Javascript/Ajax thing and doesn’t involve much PHP (if any). I suggest you ask this question in the the Javascript forum.