Instructions to browse web through latop (Windows XP) on N900:

1. Go into Control panel
2. Open “Network Connections”
3. Right click on "Wireless Connection" and click on "Properties"
4. Click on the "Wireless Networks" tab and select the check-box which says “Use Windows to configure my wireless network settings”
5. Under “Prefered networks” click “Add”
6. Type a name in “Network name” text box
7. Select “Shared” from the options under “Network Authentication”
8. Under Data encryption select “WEP” and type in your password in “Network Key” field and now click "OK"
9. Now the new HotSpot should show in the list of preferred networks.
10. Click on the “Advance” button and select “Computer-to-computer (ad hoc) networks only" and press close
11. Hit “OK”, we are done with the wireless connection properties

Open Network Connections again and share the connection which goes to the internet.

Now on Nokia N900 configure following:

1. Enter the Settings Menu and Open "Internet Connections" under Connectivity.
2. Tap "connections" button.
3. Create a new Connection by tapping "new"
4. Tap "Next"
5. Give it a name "AdHocInternet" for example
6. Tap "Next"
7. Tap "no" if it asks if you want to scan for WLAN Networks
8. Enter the SSID you entered for the AdHoc connection in Windows
9. uncheck "Network is hidden"
10. select adhoc from "network mode" dropdown box
11. select wep security method and then tap next
12. enter your wep key into "wep key1" tap next
13. now you're in the "connection: setup complete" screen. tap advanced if you have a proxy and enter it accordingly.
14. tap save on the "connection: setup complete" screen and voila

connect n900 to that adhoc network and you can access the internet via your laptop. if you set a proxy you'll have to enter your username and password.

any questions ask me via pm, will make some screenshots shortly too