Problem with attaching Archos device on Ubuntu
For adb devices to list your device (and other ADB commands to be able to work with it), you need to enable USB Debugging in your Android device. This will start the required services (the ADB daemon) on the Android device, which is what then responds to ADB commands issued from your computer.

Besides: If you are not going to use all the development stuff from the SDK, but simply wnat to interact with your device using ADB commands, you don't need to install the entire SDK overhead. See Is there a minimal installation of ADB? for details :)