I have a pretty old HDD with IDE cables, and a relatively new motherboard (ASRock 970 extreme4) with only SATA inputs. Is there an adapter or device that will allow me to connect the old IDE HDD directly to the new SATA motherboard?
So, what you are going to want is an internal adapter. You have to be careful when doing this because poorly made ones can fry a motherboard really quick. I've seen cheap ebay adapters take other components hostage as well.
I did find the Vantec IDE to SATA converter on new egg. It has a 4 out of 5 star rating across 270 reviews. If this exact model doesn't fit with your current motherboard, because of tray restrictions or space issues you can also buy the adapters that are just the wires, without the plug interface the model above uses.
The most important thing is to find a product that has a lot of positive reviews. Like I've said, I've seen some of those power adapters kill a system. So do your homework and look at the reviews. Also with these old IDE drives, remember to have the pinout set to master.