How to change default file paths

[ohadzado]

I've made custom buttons and icons in PNG format, for my new style.

I would like to place them in my /images/buttons folder as they are - without having to convert them to gif and rename to the default name.

For example, I want the button which is subsitituting 'collapse_tcat.gif' to be named 'collapse_tcat.png', and to have the system use the .png file instead.

How can this be done?

Thanks in advance!