Some older motherboards/BIOSes required manual detection of new drives or offered the AUTO setting as an alternative.
Most more recent boards just have auto-detection operable as a default drive-detection scheme in the BIOS. I would assume that auto-detection will take place...if it doesn't, then it's time to consider entering the BIOS for possible adjustment.
That covers new and old drives. If they aren't there, the BIOS doesn't worry about them...if they are, they should be properly detected.
You will have to enter the BIOS and change your 1st boot option to be the optical drive installed.
Since you are dealing with PATA/IDE drives, there is no other consideration than changing the boot option and doing the install.
Almost no other consideration
...make sure that your jumper setting for the hard drive is correct (either CS or Master), depending on your preference and your connecting IDE cables. Older IDE cables do not necessarily support the CS setting, whereas all cables support the Master/Slave setting for drives with jumpers.