KubrickHeader.jpg replaced and function.php deleted

Hello,
I recently installed wordpress 2.7.1 with Kubrick template. I didn’t want the standard blue header. I wanted to replace this with my own header. So, I followed an article that guided me how to replace the standard blue header with my own header. Part of the steps to do this, is to delete the ‘functions.php’ from inside the /wp-content/themes/default folder. But, when I do this, I am not able to use side bar to manage widgets or plugins. This is completely deactivated. I later found that, for the sidebar to function properly, I need to have the ‘functions.php’ file. So, if I have the functions.php file, the standard blue kubrick’s header overlaps my custom header. That looks so odd. I am not a programmer at all. I can only follow what I am asked to do in programming. So, keeping this in mind, can someone guide me how to achieve this? I need to have my own custom header and also the sidebar to manage plugins / widgets. Any help here is highly appreciated.

Thank you.
Mentor@Deeyes