Well I'm new too, so I guess I'll answer you, tho it's a awkward one! :)
In the book Frodo is brought to Rivendell by an Elf Lord called Glorfindel. He is then healed by Lord Elrond. The flood of the Ford is brought about by the power of Lord Elrond with the help of Gandalf.
Now in the movie, Arwen comes to the Ford of Bruinen, carrying Frodo. SHE is the one who brings down the flood. She says something along the lines of," come back into the light" or some such, and then something about Grace being passed to him (Frodo) so he would be spared. Then you see her father Lord Elrond Halfelven. I believe that here you are to assume that somehow Arwen has strengthened Frodo to survive the rest of the trip to Rivendell to her father.
Now, although I love the movie, this is my one problem part!!
Arwen is not a great healer like her father, nor is she of the High Elves, so there really isn't any reason why she'd be able to heal or even pass on ANYthing to Frodo. Still, thats just me nit picking.
I've probably completely confused you now. :)[Edited on 17/1/2002 by catz]