To compile OpenMPI against Infiniband
you only have to specify the directory where its support header files and libraries were installed to Open MPI's configure script
Build support for OpenFabrics (previously known as "Open IB", for Infiniband and iWARP networks -- note that iWARP support was added in the v1.3 series).
# ./configure --with-openib=/path/to/openib/installation
For more information on myrinet etc, do go to the FAQs.