I've purchased the Harmonics hardwood floor system from Costco for my
master bedroom. It is the same as
http://www.quick-step.com/designs.aspx?id=31.

I've removed the carpet and I'm down to the 3/4" plywood subfloor. I
have purchased 1/2" particle board for underlayment. My question, can I
get away with not gluing the particle board and how should I lay it
down? I'm currently planning to screw it down. I was shocked to find
out how much screws cost but think this would be better than nailing (I
need to address some squeaks on the subfloor first). Would drywall
screws work? Also, I plan to lay down the particle board so that
seams don't overlap the subfloor seams. Do they have to be
perpendicular or is it OK to run them parallel as long as the seams
don't overlap.

Any other advice would be much appreciated.

Thanks,

John