If you go to the product page, you can see a picture of how the full body shield covers the DS Lite. I have one and it covers almost all of the device. Certain sections of corners and stuff like the speakers and controls aren't protected; for the speakers, there is a hole in the material so it won't cover it up. The touch screen is perfectly usable and won't scratch.
When you apply it, make sure you completely clean the device (I used rubbing alcohol) and make sure you are in a dust-free environment. If you apply it and notice some dust particles, you are SOL unless you IMMEDIATELY pull it back up. Once you leave it on for a minute, it will have begun to dry and pulling it up will stretch the plastic causing it to not look as good. I had that problem the first time I put a shield on my NDS. As long as you keep it wet, you are okay.
If you have any more questions, just ask.
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For other people interested in a shield:
The covers are fully transparent (at least my InvisibleShield one is.) They don't change the color of your DS. They make it scratch proof and also makes it stick to surfaces better. It does NOT make it impact proof. If you drop it, the shield will prevent it from getting scratched, but it won't stop it from smashing into pieces.
ZAGG (InvisibleShield) offers a no questions asked (just say you need to send it in for repair) lifetime warranty and they provide an application solution for you. bestskinsever doesn't offer a warranty and you have to make the solution yourself. bestskinsever costs $11 (plus $2 shipping to the US) for their shield. ZAGG charges $25 (free shipping.)