If you are trying to disable the touchpad on the G550 then I am sure you have found that it is not very easy. There is a workaround though. By installing the Windows Vista driver and using the driver settings to disable Tapping on the touchpad while typing, you can get the desired effect you are looking for.
Warning: Customers need to uninstall the driver that is currently running in their systems before installing the new driver. Once the new driver is installed, follow the instructions below to set the Tapping setting.
1. Click START in Windows Taskbar
2. Go to Control Panel
3. Then Click on Hardware and Sound
4. Looking Under DEVICES and PRINTERS, click on MOUSE
5. Select the Tapping TAB
6. Check the setting that says: “Disable touchpad while typing”.
This will prevent the touchpad from working when the user is typing, which will help stop the mouse from moving around randomly.
NOTE: The Alps driver that is used is the same for all systems with ALPS touchpad. Basically, if the support web site for the specific system does not provide a Windows Vista driver for the touchpad, you can use the ones available for G550 and G450.
Link to Vista driver 32-bit OS
Link to Vista driver 64-bit OSLenovo G550 How To Disable Touchpad