AlpGen generates high jet-multiplicity events with gauge bosons, Higgs bosons and heavy quarks. It is a matrix element generator which allows you to match parton showers to the ME via (Fortran) Pythia or Herwig.
Finally, download the CEDAR AlpGen build package from http://www.hepforge.org/downloads/cedar . You should unpack this into the directory where you have installed AlpGen. This should create an alpint-2.1 subsdirectory. Note, there is no new code here, just the automake files to build the shared libraries with libtool. Going into this directory and doing ./configure ; make install should install headers and library for AlpGen which can then be found by RivetGun.
In the default build, rivetgun-static will not link to AlpGen even if you install it. This is to avoid confusion with other packages (e.g. Charybdis) which also use the Les Houches user process machinery. Only one interface to such a generator may be built in rivegun-static at a time. To select one of the AlpGen ones, configure RivetGun with --with-alpher or --with-alppyt. The selected interface will be built (so long as the generator, Fortran Pythia or Fortran Herwig, is also installed).
Type rivetgun-static -g FHerwigAlpGen or rivetgun-static -g FPythiaAlpGen to invoke it once it it s built.
Top Tip: By default, AlpGen prompts you for several inputs (including the name of the LHA file to read) at the command line. If you want to avoid this, look for the READ(*,*) statements in the AlpGen routine in alplib/alpsho.f. You can either hardwire them here, or if you just delete them, you can set the values via the AGILe auxilliary generator called AlpGen. This generator is used (for example) in rivetgun-static.