This instructable shows, how to change the DVD-drive of an Acer Aspire 1690 (and potentially other Acers). The pictures are low-res, but should still be helpful in finding the correct screws.
Step 1: Remove all power
Unplug the power and remove the battery.
Step 2: Remove screws at the back.
Remove the three screws at the back of your notebook.
Step 3: Remove the keyboard bezel.
From the front remove the keyboard-bezel. This is the part above your keyboard (between the keyboard and the screen). With the three screws removed, this should be quite easy.
I forgot to take a picture with the bezel attached, but here is one without the bezel.
Step 4: Remove the keyboard screws.
Remove the two keyboard screws. The keyboard is still attached to the notebook, but can be moved.
Step 5: Remove the drive-screw.
And here it is. The screw holding the DVD-drive. Remove it and the drive slides out. You might apply little force, but it should go rather smoothly now.
Step 6: Put the notebook back together again.
Going backwards, put your notebook together again. It is probably not recommended, but you might want to test the drive first.