This has been tested under Ubuntu 9.04 Gnome. The information might apply to previous versions of Ubuntu as well, but no guarantee is made.
There seem to be many different way to change the Ubuntu menu icon posted around the Web. I am posting the easiest way to accomplish this task.
Use the key combination of Alt+F2 to open the Run Application window. Enter gconf-editor and click Run.
Note: If the follow does not work, you might need to use gksudo gconf-editor.
Using the navigation on the left, click the arrow in front of apps. Scroll down and click the arrow in front of panel. click the arrow in front of objects.
Browse through the items presented under objects using the left mouse button. You are looking for the following in the right part of the window:
object-type menu-bar (Main Menu) or object-type menu-object (Menu Bar)
Place a checkmark in the value column for use_custom_icon. Double click custom_icon and enter the path to the custom icon. Click OK.
The panels should refresh, showing the new icon.
I have added below a sample icons I have created using the Ubuntu logo and added the word start afterward. This is meant for using in place of the Menu Bar icon.
I have setup Ubuntu here to have only a single bottom panel using the image above. This provides a more Windows style look.



I have reworked some portions of this post. Please try using the gksudo gconf-editor instead of gconf-editor. Please post if you still run into problems.
This was perfect until I got to “double click custom_icon”. Everything was greyed out in the dialog box, making it impossible to enter anything. I am of the opinion that I did not have the proper permission to make these changes
Hoping you can clarify and /or explain
Thanks
Barry