If you want to hack on Cabal, don't be intimidated!

Read the guide to the source code:
  http://hackage.haskell.org/trac/hackage/wiki/SourceGuide

There are other resources listed on the dev wiki:
  http://hackage.haskell.org/trac/hackage/

In particular, the open tickets and the cabal-devel mailing list
which is a good place to ask questions.