I live in a 80 year old house and the floors squeak and creek.

I saw someone's response here to a question about squeaky floors and the easiest thing to try first is to sprinkle talcum powder on the floor and sweep in into the nooks and crevices. If that does not work, you have choices based on whether the floor is accessible from the floor beneath it. Check this site that is easy to understand and has illustrations to see if it helps! http://www.wikihow.com/Fix-a-Squeaky-Floor  ; Good luck!

we had to remove the old carpet in our home and nail into the floor where old nails have maybe come out or where there weren't any.

We had berber in one house that had squeaky floors and my husband learned that if you use nails with a small head, you can nail right through the carpet and its hidden. It took several nails to stop the squeaking, but it worked and lasted the whole 5 years we lived there.

Nails tend to loosen over time and creates the squeaking. Find the area that is squeaking and install screws into the sub-floor and the floor joists to keep the floor from squeaking.

The trick I learned for squeaky stair steps was to use finishing nails and put two together crossing each other. You just need to have someone stand in that spot such that you can drive the nails without hitting a foot. Don't put the nails directly next to one another so that they don't hit. You don't need really long nails, just enough to go through the top board and about 1/2" into the bottom board. Done right, the nails won't pop up and the squeak will be silenced.