Old school is to lay them out, drill a small hole in each corner then slice across the holes and hammer and dolly. Looks rough and requires a real skill.
The other, best way to do them is to use a louver press. pics here
http://images.google.com/images?hl=en&am...mp;oq=&aqi=
The hood better be straight before this, and preferably bare metal. You really don't want to do all the prep work around the punched louvers!!!

Check local rod shops.

You also have to consider any internal structure behind where you want them. The nature of the press also requires a flat or nearly flat surface.

There are cheesy bolt-on ones that are best left to posers, and some will take an already punched section of metal and replace a section of the skin. This requires a lot of metal work the deal with the shrinking and warping.