Here is a link to the guide that will assist you installing the CD-ROM: ftp://ftp.dell.com/Manuals/all-products/esuprt_ser_stor_net/esuprt_poweredge/poweredge-1850_User%27s%20Guide12_en-us.pdf
You can mount this vertically or horizontally, the drives will work fine. Just make sure its mounted in a fashion to support the weight.
Regards,