you'll be wondering why the DS Lite protectors for the touchscreen is a little bit bigger for the original ds. though you should insert a little portion of the protector on the original ds touchscreen. they're the same size if you open the original ds's bottom half
there's a product with both the ds and ds lite screen protectors for US$4.99 (not sure for the price) in walmart as it's the one my aunt sent to me here in the philippines. it's very smooth after intense Ouendan/EBA playing. you can scratch it all you want and just apply a soaked cloth and they're gone.