Problem building the plugins package

Hello

I am having troubles building the plugins package :

manu:~/Desktop/tmp manu$ cabal install plugins
Resolving dependencies...
cabal: cannot configure plugins-1.2. It requires ghc >=6.8
There is no available version of ghc that satisfies >=6.8

I am on a Mac PPC (OS X 10.4) with ghc-6.8.2 and Cabal-1.4.0.1

so the error message is puzzling...
Can anyone help ? I'd like to install Lambdabot and plugins is one of
the dependencies...

Thanks

Manu