Editing a Microsoft template button

hello

loading up one of these buttons and dumping into word creates a button, now i can see they look like png files, but they have no background colour?

buttons ( blue ones )
http://office.microsoft.com/en-gb/clipart/results.aspx?qu=button&sc=20



now i exported one to photoshop and edited it and tried to re- import, fail, i can get rid of the background colour but it acts like a picture not a button, anyone know how i can create a new button for microsoft?

just so you get the idea - thats what i wanted