Before explain, I'm not the autor of this tutorial, it was written byswitcheremac a member of "Archos Lounge" http://www.archoslounge.net (a french archos fan website). Thanks to him.

Original post was in french, so I tried to translate it in English (I'm french).

Let's Go :

First of all you need to download the attached file "Set up google apps.zip"
- Plug your Arnova to your Computer and extract folder content in the SD Card (not the external one) of the 7b G2
- Unplug Arnova
- On the Arnova go to the file manager and install (in the order) following applications (finding in "Setup Google Apps/app/":
-1. Google Services Framework
-2. OneTime Initializer
-3. Setup Wizard
-4. Talk
-5. Gmail
-6. Vending

After that, do it in this order too:
1) Open Gmail and connect account. Gmail say it was an error (it's normaly)
2) go to parameters -> applications -> manage applications -> all
  Select "Google Services Framework" and click "Clear Data",
  Select "Gmail" and click "Clear Data"
3) Shutdown the Arnova
4) Power on the Arnova
5) Launch Gmail and enter login and password (normaly now all run)
6) That's all, you have Android Market on your Arnova 7b G2 (but that's the older one).

You can find the original tutorial in french here : http://www.archoslounge.net/forum/showthread.php?t=23623