I put down laminate floor a few years ago in my kitchen and family room, but before I did I removed the carpet and pad in the family room as well as the tack strips. I recommend that you first talk to an experienced installer and ask how to carefully take up the entire laminate floor. The vinyl floor covering doesn’t have to be removed but the carpet pad and tack strip does. Go over the floor and firmly nail any place where you may have a creaking floor, use a good nail that will not work its way back out of the wood. Then lay down an underlayment that is recommended for laminate floors. It is a thin vinyl like material and can be purchased at Home Depot, Lowes or any flooring store. There are a couple of grades of underlayment, dont go cheap on it. While you are at the store ask an experienced sales person what type of nails they recommend. I believe I used a good galvanized nail, don’t remember the size. After you have all this done put your laminate back down.
PS
I don’t recommend having your friend do this for you; he didn’t do you any favors the first time.
Mr. Hammer, November 2007