There are mix and match of about 5 different types of clips/fasteners that hold the grille in...depending on what year you have.
There are the 2 piece type that have the plastic "pin" in the middle of them. To remove them, you push the center pin in about 1/8", then that will release the fastener where you can get something under the outer edge of the head and pull it out. To reinstall it, you pull the center pin out, put it back in the outer piece, until there is about 1/8" of the pin sticking out, push the fastener in the hole, then push the center pin in flush with the outer piece.
There are the 1 piece type that just push in. Usually, you can get something under the head and pull them out. But sometimes they will pull in two, or strip the outer "hairs" off and they won't hold when you reinstall them. To reinstall, you just push them in the hole.
There are a couple of variations of the type that djlantis57 was trying to find. They are plastic and the one type will usually break every time the grille is removed. The other type, you can usually take a thin flat blade screwdriver and gently push down on the center "hump", so as not to break the clip or the grille, and gently pull on the grille and it will pop out (the clip stays in the grille surround).
Then there are screws. Pretty self explanitory on removal and installation.
As some of you have noted, some of these can be found at auto parts stores or other places. And some are next to impossible to find.
When I was looking for the 1 piece type that just push in and pull out for my Ranger, I could actually buy them cheaper at the dealer than at the auto parts store.
BTW, djlantis57, excellent find on the metal clips. Those should last forever and look like the grille should be much easier to remove than with the plastic clips.