i've done a few of the ds lite in the past and they are quite fiddly with the top screen ribbon (you have to loop it through a small ring on the hinge) but if you take your time its easy enough to do. I'm sure you're in good hands with Roy
Done about 300 DS Lite re-casings in the past (had a little business going for a while back in the day). Can offer my services if you need them.
Scrappy - There is definately a method to the top screen ribbon, the key is not to be too "careful" believe it or not.