ok,,i asked if I lay plywood over the existing particle board as explained in another post wont I get alot of bounce and uneven surface from where the particle board had dipped between joist? Do I need to lay a moisture barrier on top of the old particle board before laying the new plywood?? Any help appreciated.

What kind of floor are you installing? You can put laminate or hardwood directly on top of vinyl - it makes an excellent moisture barrier. You'll need to put some kind of moisture barrier over the particle board... 30 lb. tarpaper is recommended. The flooring is installed on top of the tarpaper.

I didn't see your original post, so I don't have any suggestions about the sagging portions of the sub-floor. You may want to just replace it.

thx

I had stated previously to another person, I have installed porcelain tile in my dbl wide and hardwood. In the family room rather than using backerboard, I just used the tarpaper (roofing paper) and then put the thin set on top. It is a moisture barrier and trade-show trick - you can remove the tile later without tearing up the entire subfloor by jack-hammer. You need to nail the backer board/hardy board to the sub floor about every 6-10 inches / then seal the cracks with tape which is made for doing just this type of thing. For installing hardwood, you do not need to put additional flooring on top of the subfloor if you are using adhesive rather than nailing.
Hope this helps also.