When you say "just the outer painted part of the insert", are you talking about the whole scoop insert in the hood, removing the insert and painting it ?
Anyway, a few considerations. The insert is composed of several parts. The scoop itself, a mesh screen and a "cup" behind the screen. Do you want to paint all of them or just the scoop insert ? Either way, you should take the whole scoop assembly apart and pull the "cup" and screen off.
To paint the scoop, I'd recommend sanding first with an 800 grit sand paper. Thoroughly sand it. I'd recommend then "priming" with a good adhesion promoter, such as Bulldog. Then paint with a good quality basecoat paint and clear coat (or you can go with a single stage urethane that essentially combines the two together). Keep in mind that if you're painting this all in your garage, in an uncontrolled environment (i.e. not a paintbooth), then you will likely have to color sand with 2000grit paper to get rid of trapped dust that lands on the paint while drying.
If you've never painted like this before, I'd strongly recommend painting scrap pieces first to perfect your skills before moving onto your scoop.
Here is a thread to consider for painting. It's a whole lot more involved and way, way, way more complex than what you're after, but it gives an idea of the work that may be involved.
http://www.xr-underground.com/vb3/showthread.php?t=22155&highlight=blackcat+reborn
