Just install it inside the C:/Program Files/Rockstar Games/Grand Theft Auto IV/common/data
The Dashboard view is replacing the hood view/trunk view.

Known bugs:
If you hit something, you'll probably see a bit Niko's head (but it's as far as I can go without loosing interest of a "dash" view.
For certain vehicles, the view isn't that great (it's playable but almost useless).
Maybe something else but I have checked each and every vehicles and they look OK.

Credit to Krazymond
Made on version 1.0.1

IMPORTANT : Don't forget to unlock the game for modding (search for "modding patch" like the patch here
http://www.gtaforums.com/index.php?showtopic=380102
(you can find several different version)