Narya

[Sharkû]

Did Narya help Gandalf with Theoden? Could it have had any influence over the Ents?

Most definitely, I would say.
The Ents may be a more difficult case, since Gandalf was not personally present at their rousing. Or was he? I for one never quite believed his denial to the Three Hunters that the wizard they saw outside of Fangorn was not him.
But the healing of Théoden and the rousing of the hobbits seem like good evidence to me. Gandalf literally rekindled the hidden valor of the Shire-folk, vital to the quest, like a bright new spark that sets ablaze a long smouldering ember, to shake "fields to shake the towers and counsels of the Great" (Elrond). The latter quote also reminds, when taking out of context, of the Ents.

The healing of Théoden by Gandalf the White is even more obviously an effect of Narya, too, for here we have all the signs and symbolisms of the Ring of Fire.
At first Meduseld "seemed dark and warm" and "filled with shadows and half lights" . The sky above is pale, but yet some sunbeams reach the ground, the signs of coming change.
"But upon one form the sunlight fell: a young man upon a white horse" - a portent on the rise of Théoden, like his ancestor, and his people. The King himself is bent and seems decrepit, but the ember that could be kindled could still be seen in his eyes. The staff he leans on, black with a handle of white bone, is a symbol of death, and at his feet sat Wormtongue, tormenting his master's mind like a nightmare that sits on his breast.
As Gandalf casts his cloak aside and reveals his power, the scene changes to an impressive climax:
"He raised his staff. There was a roll of thunder. The sunlight was blotted out from the eastern windows; the whole hall became suddenly dark as night. The fire faded to sullen embers. Only Gandalf could be seen, standing white and tall before the blackened hearth" (my stresses).
The rage of the new fire of Gandalf extinguishes the old, sickly, smouldering fire to light anew a fire from the still underlying old and pure flames. The contrast of light and darknesses is obvious -- Gandalf himself becomes the fire of valor.
After that revelation, the scene is totally new: "There the darkness seemed to clear, and through the opening could be seen, high and far, a patch of shining sky. 'Not all is dark'". A faint light grows again in the hall, outside a fresh breeze drives away the clouds just like Gandalf drove away the mental cloud on Théoden that was Gríma. The abttributes that return to him, clarity to his head, and strength to his body, are all associated with the element of fire.
And what Théoden perceives as a fire that will "devour the high seat" is the bright new flame that will prevail over the enemies of Rohan, but also the life-flame of Théoden himself, which rises high in his last days, but eventually vanishes as he is overcome by a greater darkness on the Pelennor; his fear that overbold moves would threaten Rohan in the current situation - for this is also one thing he undoubtedly meant with this sentence - is quickly dismissed by Gandalf; the new great flame that is in the Hall will not harm the seat, but rather defend it.

[ November 24, 2001: Message edited by: Sharku ]