I want to use meteor slides plugin but don't know where to insert the code in atahualpa (version 3.7.12)...

have you searched the forums?

yes, I did and came up with this thread

http://forum.bytesforall.com/showthread.php?t=15767

but I can't seem to make it work...

Yes I did and came up with this thread

http://forum.bytesforall.com/showthread.php?t=15767

It says

So remove the code '<?php if ( function_exists( 'meteor_slideshow' ) ) { meteor_slideshow(); } ?>' and put in the new widget area code, add a text widget to the new widget area and add your code to the text widget.

But I haven't figure out how to do that...

The documentation in the theme for creating new widget areas takes a bit of study to understand but is pretty complete.

I figured it out thanks a lot!