Changing dynamically the Picture in a PictureButton control

How can I change dynamically the picture assigned to a PictureButton control?

I'm using in a script:

button.PictureName="c:\resource_directory\newpicture.bmp"

and I have a reference in the resource file to "c:\resource_directory\newpicture.bmp", but it doesn´t work in the executable files, if I don´t have the c:\resource_directory\newpicture.bmp, in the client computer.

TIA

AUGUSTO