I have a habit to use testing branch of debian. Currently it’s Lenny.
The problem is, gcc package now is version 4.3. The g++ of that version is stricter (being transitioning to C++-0x), emitting errors when compiling rubinius c++ vm. The solution (workaround, actually) is installing the 4.2 versions, then replacing the gcc and g++ symlinks (prvided by gcc and g++ packages, respectively) to point to gcc-4.2 and g++-4.2, respectively. Yes, it’s a hack.