I have two hard drives on my primary IDE and two CD/DVD ROM drives on my secondary IDE. I would like to add another hard drive. Is this possible with this configuration?
No. Good Luck finding an IDE cable with more than 3 connectors on it. Also, you only have selections for Master and Slave.
You can add a PCI / ISA card with an IDE interface on it to add two more ports. You can also add a SCSI card, and add more drives that way. Or find larger physical drives, and condense them.
Be careful adding so many devices though... your power supply might not like it. Yes, you can physically add more Y connectors to the power leads, but that costs amps, and you need to avoid an internal brown-out.
Good point about adding too many devices. I do need to be concerned about power consumption. That leads me to another question. Assuming that I am not using any Y connectors, does having an available power connector imply that I can probably "afford" (in terms of power, not cash) to add another device?
Not necessairly, but you should be alright.
You have to work with the rules of electricity here. Somewhere on your power supply, you should be able to see what the output power capabilities are... 12 V @ 5 amps, or 5 V @ 5 amps. Remember high school physics: Amps * Volts = Watts. Whatever rating your power supply is... that is the supply.
Add up your external devices... those are "draws". All hard drives. The mother board. USB devices.
Supply - Draws = spare.
If spare is a negative number, you are in trouble. If spare is within 10 percent or so of supply, I would say you are in trouble.
I would "guess" that if you have another free connector, that you could put something else in there. BUt if you want to do it right, then do the math.