Eclipse is a great IDE to program/debug multiple languages, such as C/C++, Java, etc. To using openmpi on Eclipse, you need to install PTP (http://eclipse.org/ptp/downloads.php), or directly install Eclipse IDE for Parallel Application Developers.
Once I installed PTP on an existing Eclipse indigo, I can directly create an “Openmpi C++ project”. However, some MPI functions are still not recognized by Eclipse, such as “MPI_Init”. That’s because your Eclipse does not know the include library path of openmpi. Two way to add this path, (1) Project->properties->C/C++ build->settings, under GCC C++ compiler and GCC C compiler ->includes, add the location of the openmpi library path, mine is /use/lib/openmpi/include. (2) or change globally, Window->Preferences -> Parallel Tools ->Parallel Language Development Tools -> MPI Include paths, click new and add your openmpi include path.