Acer Aspire 1642 Disassembly Manual page 9

Fig. 11
At this point I bent one of the metal tabs on the top cover so that it gave a tighter fit, and re-assembled.
If you want to take the CD/DVD tray apart further you will either need to go ahead and take out some
screws etc... (and write a guide while you are at it!) or find another guide which covers taking these
things apart.