I've been asked to use that before and have done so. It's fairly cheap and easy to use, but I question the effectiveness. The floor would be nailed through the cork into the subfloor, effectively transmitting impact noise to the subfloor via the nails. It might be more effective with airborne sound transmission than with impact sound.

Use black roofing felt paper($20 a roll). Been using it for last 10 years without any issues.

If by noise from creaking boards. Only a well secured floor will stop that. Until it ages but then its fair game. Cork wont stop that.

It will dampen noise from walking or rolling things across the floor. Wont eliminate it.

One thing to consider is if it is a nail down product (the floor) then you need to think about the length of staple or cleat to use. A standard 2" cleat wont secure the floor well enough through cork. That extra height the cork has takes away from the amount of bite the cleat will have on the subfloor. Not a huge issue in terms of price but its an easy oversight that some may not think of.

Thank you all for the feedback.

GregMills...thank you for the tip. While I'm not actually installing the floors myself (I don't trust myself enough), i can see how that could be really easily overlooked.

I do have another question.
Upon removing the original 1940's hardwood floors, I'm wondering if anything needs to be done to the subfloor before laying down the solid hardwood. I keep reading that hardwood floors should be laid over plywood...but our subfloors look a little different.

Any advice?

Plywood wasnt invented when your house was originally built or at least wasnt the "norm". I dont know the exact year plywood was invented but its real common not to see it in a house of the 40's.

Its perfectly acceptable to install hardwood over that.

One thing to look for with your type of subfloor is spongy spots. And to be sure all the boards are securely screwed to the floor joists. Otherwise it should be good to go.