I am putting in a new laminate floor and wonder if this will stop any squeaks I have in the floor now? Do the existing squeaks have to be repaired BEFORE the new floor is put in?

Yep, repair the squeaks now, they will diminish with the new floor but won't go away. What is your current flooring material and sub floor?

Yep, repair the squeaks now, they will diminish with the new floor but won't go away. What is your current flooring material and sub floor?

From deliticket: The sub floor is Douglas Fir over plywood.

From deliticket: The sub floor is Douglas Fir over plywood.

I wound screw the Douglas down with screws that are 1.5" longer than the thickness of the fir and plywood. If you really want to do this right there should be a screw every 8" in all directions. It will not squeak any more. Go to the home center and find the Hardobacker subflooring material. They have self tapping underlayment screws, square drive, that I have found to be great for your application.

If Possible You Should Try And Find The Floor Joist And Use Screws No Nails.
If You Have Access To Under The Floor Just Drill A Hole From Underneath Beside A Joist, They Should Be Every 16 On Center.
This Will Stop The Squeaks If Its Coming From The Subfloor, If It Is The Douglas Fur Floor Squeaking Then A 2 1/2 Screw Will Work Fine, And 8" As Said By Ballengerb1 Is A Good Place To Start