Hello

To open up the case you should follow this guide.

http://www.llamma.com/xbox360/repair/Xbox-360-Disassembly.htm
complete with enlargable pictures.

That tells you how to get to the dvd drive.

To open the dvd drive there are 4 screws near the legs or 6 if you have a hitachi drive.

Remove the bottom plate with encouragement and with a little encouragement the top plate will come off too allowing you access to the dvd drive laser