I got this thing to work eventually, everything you need to know is in this thread but there is a lot of stuff you don't need to know too so I hope to get this right first time. This is, I hope the definitive how to create ad hoc capability on your Samsung Galaxy Tab 10.1 without any noob confusion. There is some cut and paste from the thread here so thanks to the original authors.
Follow all these steps.
You will need;
1. a rooted SGT 10.1 - Do this by searching the forum for instructions. Do this first
, then come back here and continue. [I do not know if or how it works on other devices - DON'T ASK
2. ES File Explorer from the android Market
3. Download hacked the wpa_supplicant from this post
to your SGT. [If you visit the page with your SGT, the file will download to 'home>download' on your device, if not, put it there yourself so it can be found later]
ONCE YOU HAVE ALL THOSE THINGS, CONTINUE...
4. Open ES File Explorer and in settings menu select Root options. - menu>settings> tick root explorer and mount file system - say yes to popup.
5. Click the home button to get to your SGT home screen, tap the battery/wifi indicator at the bottom right of the home screen, select settings>wireless and networks and tick flight mode to on. [You can reboot here, it won't hurt]
6. Make sure airplane mode is on
then using ES File Explorer on your SGT, navigate to 'system/bin to find the file called wpa_supplicant, do a long press on this file and select rename, keep the name but add .bak or.old to it so it is now called wpa_supplicant.bak or wpa_supplicant.old
7. Using ES File Explorer on your SGT 10.1 navigate to home>download and find the wpa_supplicant_wifi_adhoc folder, click it once to open it, long press on the file called wpa_supplicant and select copy.
8. Using ES File Explorer on your SGT 10.1 navigate back to system/bin then long press on an empty part of the screen and select paste. You should now have two wpa_supplicant files, one called wpa_supplicant.bak or wpa_supplicant.old and one called wpa_supplicant which is now the hacked version.
9. The wpa_supplicant needs to have the correct permissions to work properly so tap it twice, [don't open it] then with the file highlighted tap the file menu [3 lines at the bottom of the screen] select operations>properties>change, there are 9 boxes, make sure there is a green tick in all of the read column, all of the write column and the top line in the execute column. Like this
X X X
Click OK twice. [You can reboot here]
10. From the SGT home screen tap the battery/wifi indicator at the bottom right of the home screen, select settings>wireless and networks and tick flight mode to off. Turn on your phone's wifi sharing and hopefully your SGT will find it.
That's it. This is how I did it and it works with my Nokia N8 using Joikuspot premium, it should work with the free version too. GOOD LUCK!