Boni, as you post it now, I assume you have Blender 2.44? That requires Python 2.5 and someone recommended actually 2.5.1 which works for me.

For clarification:
Blender 2.43 and earlier required Python 2.4.
Blender 2.44 requires Python 2.5.

...and Blender 2.44 is quite recent so what you read earlier in this thread is no more accurate for 2.44. Python install is very important for 2.44, even more important than for earlier versions.