Looking at the specs on the 1100 Dell Dimension, you seem to have two 5.25 drive bays, one of which is being used by the original cd or dvd drive that came with the machine. You should be able to take the cover off the second drive bay and put in another optical drive, or simply replace the one that is there.
I suspect you have a regular IDE interface drive in a machine of this vintage. A good replacement would be a Pioneer 115D
You will have to set the jumper on the back of the drive before hooking it up to the IDE cable. Set it to CS (cable select) since this is the usual method that Dell uses for IDE devices.