This is an adaption of a script that I found (not sure where now but possible to re-find by searching on google). The name under the registration was Lucas Pettett so I guess it was his.
Originally it took some colours and text and produced a vista style button with a gradient dark part and light part horizontally divided. The corners were rounded and it had a border.
I have added the following things (so I can quickly create buttons for some of the applications I am working on):
I'm not a script-fu programmer so most of this is trial and error and would probably benefit from some expert scrutiny.
The GIMP I'm using is 2.6 on windows so I don't know if it works elsewhere.
(examples attached below)