Installation:

Before installation, install Dreamsky's Smart car.
http://www.gta4-mods.com/vehicles/2012--smart-fortwo-f14378

1: Extract ukip.wtd

2: Rename it to the name of the vehicle the Smart ForTwo replaced

3: Add it to C:\Program Files (x86)\Rockstar Games\Grand Theft Auto IV\pc\models\cdimages\vehicles.img