The Ubuntu Hardy repository has been dropped and replaced by an Intrepid repository. If you need the bluefish-unstable package for an Ubuntu Hardy installation, keep the deb-src entry from the previous sources.list snippet, get the source and the build-dependencies. Then build the package(s) and install them.
apt-get source bluefish-unstable apt-get build-dep bluefish-unstable cd bluefish-unstable-version debuild -us -uc ... dpkg -i package.deb
The same goes for building the package for a different architecture than i386!