Yeah there is the so called GimpShop (link: http://plasticbugs.com/ ) I guess you mean that.

However I just tried that plugin I posted above with the GIMP 2.2 version but opening an image does not work anymore.

EDIT #1:
After testing the 3.0-alpha version of the plugin which did not work for me I just tried the 2.1 version.
Unfortunatly this version does not transfer the gimp windows into one big window and is really just a background plate.

EDIT #2:
For everybody who likes GIMP but wants it integrated into one window: Try GIMPshop:
http://plasticbugs.com/?page_id=294

(Scroll down a bit for a windows version, I'm currently trying out this one: http://www.plasticbugs.com/blogimg/GIMPshop_0.1beta_Setup.exe )