Remove the grapes from the vine stem-thingies and wash thoroughly. You want them nice and wet so the gelatin powder sticks to them.
If you want to do this the hard way, place the gelatin powder on a plate and use two spoons to roll grapes into the powder, completely covering. Or if you want to make your life easier just throw the powder in a zip lock bag, drop a handful of grapes in at a time, and shake until covered.
Refrigerate for several hours. I left mine in the bag to refrigerate them. If you do this, the sugar on the outside will never dry out and your grapes will stay wet. The best way to do it is to lay the grapes out on a baking sheet, uncovered. Try to keep the grapes from touching each other too much. This will make them nice and crunchy on the outside.
Notes
You can use any flavor of jello that you want, and red grapes would of course work fine. Let me know what other combos you come up with! Also, I don't like frozen grapes, but if you are into that I've heard these taste great frozen.Source: Sweet Treats and More