I needed to apply the follow patch to packedstring to install it with ghc-6.12.1 and cabal-install-0.8.0 on my machine:
diff -u packedstring-0.1.0.1/packedstring.cabal\~ packedstring-0.1.0.1/packedstring.cabal
--- packedstring-0.1.0.1/packedstring.cabal~ 2010-01-17 16:23:32.000000000 +1000
+++ packedstring-0.1.0.1/packedstring.cabal 2010-01-17 19:18:15.000000000 +1000
@@ -9,7 +9,7 @@
(Deprecated) Packed Strings.
build-type: Simple
Library
- build-depends: base, array
+ build-depends: base >=4, array
exposed-modules:
Data.PackedString
extensions: CPP