To allow ad-hoc access in Android, here is a hack I've found in the net but I haven't tried it yet. Just sharing. I just got Archos 101 and started tinkering with it today. I can't seem to enable internet access by Bluetooth and Tethering with my Nokia E72 phone.
"I did it manually... Check the ROM for files for "RT2870STA". It's in there, 3 or 4 times the same file. Open the android_fs.tar and the data.tar as well!! Use 7-zip to browse the archive, or you can unpack these *.tar files to a seperate folder and then search for "RT2870STA". Open the RT2870STA.DAT files with a texteditor and replace "Infra" for "Adhoc". Close the files and choose save. Then go back to the *.tar files and browse them again with 7-zip. Copy the edited files to the right folders (overwrite the .DAT files) and copy your complete script folder to your SD card. Insert it into your tablet and then turn it on... You must enter the SSID manually in your tablet because it can't find the SSID of your Adhoc network by itself!"
Source: WiFi Ad Hoc Network Not Found