[Haskell-beginners] Question about ghc and cabal: finding packages

Hi everyone, I have installed ghc 6.12.3 and the Haskell platform; now, when I install packages from hackage using cabal install <package-name>, they get installed in ~/.cabal, which is fair enough. However, when I call a runhaskell Setup.lhs configure that used to work on a different computer with the same software setup, ghc (or is it cabal?) complains that it cannot find the packages I have just installed. Checking again revealed that they are indeed installed, just not in the ghc installation directory, but under ~/.cabal. How can I tell cabal and/or ghc where to look for libraries? Thanks, again, for any help! Christian