I managed to install wxMac2.8.7 (I could not get 2.6.4 installed on my 10.5 Leopard machine, Intel MacBook), and managed to compile wxHaskell 0.10.3 against it. Unfortunately the helloworld bombs:

loeki:wx doaitse$ /usr/local/wxhaskell/bin/macosx-app -v Helloworld
creating resource:
 > /Developer/Tools/Rez -t APPL Carbon.r  -o Helloworld
creating app directories:
 - Helloworld.app
 - Helloworld.app/Contents
 - Helloworld.app/Contents/MacOS
 - Helloworld.app/Contents/Resources
creating package info:
 - Helloworld.app/Contents/PkgInfo

loeki:wx doaitse$ open Helloworld.app
LSOpenFromURLSpec() failed with error -10810 for the file /Users/doaitse/Software/wxhaskell-0.10.3/samples/wx/Helloworld.app.
loeki:wx doaitse$ 

Anyone an idea how to proceed?