Agreed with Citadel. Connect it up, and see what happens. Unlikely to do any harm, and it should just be recognised without any trouble. If it is a DVD rewriter, it'll still be recognised, but you will need a software package to write disks.
I have just noticed that the harddrive is set as master,and the cdrw as slave.The CDRW will play cd's,but with not record.When the DVD ROM is installed both drives are set as salve,but when you eject one drive,the other is ejected as well.
With this config both drives and harddrive work,but with issues.