Just as a side note for others (since this was a really old question)...
The original Archos SDE could not be installed on Archos G9 tablets that had already been upgraded to their 4.0.2x firmware version. It only worked with for those that still had 4.0.x (such as 4.0.5, 4.0.6, or 4.0.7).
However, supposedly several months ago Archos did upgrade their SDE so that it can now be installed on G9's that had been upgraded to the newer 4.0.2x firmware. They also now supply an SDE for their G10 devices as well.
Since Archos really dragged their feet for months on doing it though, most of us had already found out how to install an UN-official SDE (thanks to the great work of people over in the Gen9 sections of the xda-developers website