The link to the gtk2hs website doesn't work any more. Does anybody know where that site ended up? It used to be at http://www.haskell.org/gtk2hs/.
Installing gtk2hs - GTK+ and Glade troubleshooting
The version of the GTK/Glade bundle in the wiki link is older than the recommended 2.22 bundle version. Cabal fails to build against the old version.
See: http://www.gtk.org/download-windows.html and download the latest zip GTK+ All-in-one bundle to build gtk with success.
Also, the gtk2hs set of packages have a bug which prevents cabal package registration.
See: http://hackage.haskell.org/trac/gtk2hs/ticket/1203 for the resolution.