Eriol said:
Galadriel there appears to be teasing
Frodo as opposed to REALLY tempted by
the Ring; I get the feeling that she already made that decision, when the Ringbearer first stepped in
Lórien (this would of course where temptation was felt; there was no strict need to wait till Frodo offered the Ring to be tempted by it). Movie-Galadriel apparently is quite moved by the offer

.
You are forgetting what is really at play in that scene. It has nothing to do with the choice to take the Ring or not to take the Ring.
It is the choice to maintain
Lothlorien, or to accept the Doom of the
Noldor.
Remember that Galadriel is much older than any other
Elf in
Middle-Earth at the time. Even
Elrond and
Glorfindel are younger. Galadriel lived for a while in
the Blessed Realm. She was born to
Finrod either during the Exodus to the Blessed Realm or during
the Golden Age of
Valinor. She was one of the noble
Elves that led the Noldor through Helcaraxe into
Beleriand after the Kin-Slaying.
Now there were two things that
Mandos pronounced when the Noldor left. The Doom of the Noldor, and the Curse of the Noldor.
The Doom of the Noldor was that they could not re-enter the Blessed Realm. Hence why Galadriel was STILL in Middle-Earth. She could not return.
The Curse of the Noldor was that all that they did would turn to ruin as they tried to regain
the Silmarils from
Melkor. Galadriel was spared from this, as it applied only to those involved in the Kin-Slaying.
Hence why she used Nenya to create Lothlorien. As a shadow of the Blessed Realm that she could not go to. She had lost all her family as well, all she had left was the people of Lothlorien. We can assume that these were also Noldor who were not directly involved in the Kin-Slaying.
If the Ring was destroyed, or went to anyone other than Galadriel, Lothlorien was destroyed. And once Lothlorien was destroyed, she was stuck in Middle-Earth unlike the other Elves. So she wanted it badly. She admits thinking about such a chance many times in the book. The only chance to save Lothlorien was to take the Ring for herself.
Why did she not take it? Look to her words. She considers what she would become if she took the Ring. Powerful, and terrible. Then the thought enters her mind. By refusing the Ring she has a hope at least of having the Doom of the Noldor repealed in her case. And she takes the chance.
She has a MUCH more involved choice than what the book even shows. You need to read the Appendices and
the Silmarillion to appreciate the scene.