How can I install an addional (second )DVD drive
Starting on page 55 of http://www.manualowl.com/m/Acer%20Computers/Aspire-E700/Manual/114116 you can see the diassembly instructions with pictures. Use as much of the guide as you need, but when you take the case off you'll be able to see the HDD and the first optical drive connected to the front of the computer. If your system is identical to the one pictured, you'll need to remove a little cover directly under the primary disk drive. Then slide your new drive in from the front until it slots into place (there may be screws to hold it into place). According to the manual I linked, you should have a few extra SATA ports on your motherboard (the primary disk drive and/or harddrive should have one coming out the back. follow it to where it leads and you'll see other similar ports to plug your new wire into). If it's not SATA, it's IDE, which is a wide, flat cable (approx two inches wide). The principle is the same regardless...Find the port to plug it in, then plug it into any available SATA/IDE port. Next, plug in the power cord (should be a 4 wire plug if IDE, or another flat cable similar to the SATA cable, but wider). Once that's all hooked up, reverse the disassembly instructions you followed, put the cover back on, and boot it up. Most drives are plug and play, so you shouldn't need to worry about installing any drivers or anything. If you do, just install them like you normally would, restart, and you should be good.
Good luck, and it's much easier than you might think at first :)