I know you side that you've searched here, but the 'Create Soft Glassy Buttons'
tutorial seems pretty good, and maybe also the 'Orb-Icons For Websites'. Just
reading through them might give you some ideas on how you could make the exact
style your after. I hope that helps.
http://www.gimpusers.com/
The internet is replete with video tutorials on how to create "shiny" or
"glassy" Vista-style buttons primarily using PhotoShop. As a user of Gimp for
the past 8 years I searched here and other Gimp sites for a WRITTEN TUTORIAL,
not videos. Over the years I lost what I thought was the best step-by-