Great forum and thanks for your help in advance...

22'x22' master bedroom over garage 2/12" 16" OC. I have a 1/2 CDX subfloor with 1/2 particle board on top.

I tried pulling the particleboard, but it's 8d nailed with glue. I wanted to pull the particle board, as I hate the stuff, but, looks like I would have to pull up everything, which would be a pita. I have the ceiling height (Doors dont matter as I am replacing all of them) Can I get away with skinning over the top with 1/2 CDX? I am looking to 2" cleat the wood in place. Or, should I go with 3/4 T&G ? My concern is having enough "bite" for the cleats. Am I worrying for nothing ?

Thanks for your help everyone

P.S. Pulled up carpet.. previous owners had cats..ummm a few stains on the particle board. Don't want that fragrance coming back... can I paint over the top of it with Kilz to "seal" it in?

Being over a garage you shouldn't have any moisture concerns. Particle board is not ideal for nailing to,but it's possible as long as it's in good shape and has no water damage.
If you install another subfloor over it, it'll still be attached to the particle board, and if it ever gets wet, it's coming loose.
I would use 2" staples,not sparingly, and nail to the particle board. If it's 1/2" thick then the staples will reach about 1/4" into the first layer of subfloor.
I've installed tons of hardwood on PB with no trouble, as long as no moisture was present.

Thanks for the reply FloorPro,

Keep in mind that the original subfloor deck is 1/2" CDX with a layer of 1/2 Particle Board that is glued and 6D nailed. I plan to go over the top of this with 5/8 CDX and use Durock Pan Head Screws and glue, tieing the whole structure down to the 2/12's. The existing PB has been in there since they did the addition in 1982. It's clean and secure and will be stable. I intend to add quite walk or a similar membrane on top to seal it, potentially with 6M Visqueen as a barrier, just in case there ever was a leak. (Although, there is no water in the area and the entire roof was replaced last month.

Will go with the staples.. reading up and tend to agree with you on that, after reading the whole thread on fastening.

Thanks for your time and anyone else who can provide some experience and suggestions