I recently had to replace a cracked top screen of a Nintendo DS - the replacement part was less than 10% of the cost of buying a new one. I had read very briefly that it was "a little fiddly", but not too tricky, so I just ordered the part. Only after it had arrived and with screwdriver in hand that I realised the scope of that fiddlyness.

[Image of DS in many parts]

I followed the excellent thirty minute guide here: http://www.youtube.com/watch?v=5a1AIWYXPmg and it went almost without a hitch. Just two things to add.

• The replacement screen flickered, and I thought I might have replaced the cracked screen with another defective one. It turned out that I just needed to calibrate it using two tiny screws under the battery compartment. It is easier to do this before fully re-assembling the DS, at the point in the video where the friendly Australian chap suggests testing it.
• The video doesn't have a high enough resolution to see what is happening when he is "flicking" the connector where the top screen's ribbon attaches. You need to be careful when forcing such tiny parts, so note that there is a bar which you flick down to disconnect the ribbon. When you're pushing the replacement screen's ribbon in, be sure to push it all the way in (and don't close the bar, which just pushes it back out).

[2x images of connector]

Anyway, DS fixed.