if you have an extra bay then u can put the new drive in and use both. just set one as a master and the other as a slave.(so long as u have a means of conecting both to the mobo)
Virtual all DVD drives nowdays will read CDs aswell. Check the front of the DVD drive for the "Compact Disc" sign or on one of the stickers. You should be ok even if its not there.
Almost all DVD RW drives are 6 in 1, they read, write, re-write DVDs, and same with CDs, so you don't have to worry about this. If you are talking about drives connectivity to the mobo, I think this has been already answered.
