Default Maemo kernel doesn't have some modules, so it must be replaced with titan's enhanced kernel which could be also used for overclocking N900.

Next step is to install iptables and wireless-tools with mobilehotspot.

The easiest way to do is:

1. connect the phone with internet (wi-fi or 2G/3G);
2. enable repository extras-devel in Application manager and then close Application manager;
3. open X Terminal;
4. type sudo gainroot and confirm it with enter key;
5. this step is not necessary, type apt-get update and confirm it with enter;
6. type apt-get install iptables wireless-tools mobilehotspot and confirm it with enter;
7. after installation is done, type reboot to restart the phone;
8. open mobilehotspot, set WEP Encryption password (5 or 13 characters), Network name and Connection, but do not be connected with internet;
9. then press on button Start to start with wi-fi tethering.