You need Rhino4 SR9 or a recent Rhino5 Beta to run Grasshopper.
Note that you need the most recent Microsoft Runtimes to be able to run Grasshopper. You can download the latest runtimes from the Microsoft Website and be sure to get the 32-bit ones (vcredist_x86.EXE).
Danny Boyes
This from the 0.8.0052 Thread
Nov 16, 2011