The most popular robot that made it on another planet was the Mars Pathfinder. It's pretty much something that you would see at a science fair with a few modifications to meet environmental constraints.
The Mars Pathfinder used the VxWorks Operating System. The hardware was a IBM 6000 RISC processor with 128MB RAM. The software was written in C and Assembly Language using the XLC compiler from IBM.
You can get more information about the physical characteristics of the Mars Pathfinder at:
http://en.wikipedia.org/wiki/Mars_Pathfinder