In 3.5, unless my SRD has errors, hold person contains the following "The subject becomes paralyzed and freezes in place. It is aware and breathes normally but cannot take any actions, even speech." Thus, a held person in 3.5 cannot in fact delay or ready an action, or indeed do any action including purely mental ones.
Also, the paralysis entry has the following text :"A paralyzed character cannot move, speak, or take any physical action. He is rooted to the spot, frozen and helpless. Not even friends can move his limbs. He may take purely mental actions, such as casting a spell with no components."
Thus, it is certain that you can delay while paralyzed, and assuming my SRD is right, you probably can't while held (there is a contradiction in that hold person says you are paralyzed though). It used to be the other way around in 3.0, no ?
I'm not 100% sure readying an action is purely mental though.