Disable Unsigned Driver Dialogue

First Go to: Start --> Run

Then type: gpedit.msc and hit enter. Browse the folder tree to the following location

User Configuration --> Administrative Templates --> System. 

1. Right-click Code signing for Device drivers and select Properties . 
2. On the Settings tab , either select  enable, and then select ignore from the appearing listbox or click the disable option. 
3. Click apply and Ok and your set!

Alternatively especially for XP Home users:

1. Open "System" properties (Windows key + pause or Right click 'My Computer' -properties or Control Panel - System).
2. On the Hardware tab click the "Driver Signing" button .
3. In the dialogue that comes up choose  " Ignore " to install the new driver anyway.