On which finger had frodo the ring, when gollum...

From what I know of tradition and culture, any ring that is not a wedding or engagement band is worn on the right hand on the Ring Finger. There seems to be some confusion as to what this finger is. I will explain it. Hold up your right hand. At the far left is the thumb. Next is the Index Finger. Then the Middle Finger. Then the Ring Finger. And finally the Pinky finger. If the ring is a wedding or engagement band, then it is worn on the Ring Finger of the left hand. I have a High School ring and I wear it on my right hand on the Ring Finger. This should stop all contestation as to which finger the Ring was on. As to the Sauron question I like the Movie's interpretation, where as Sauron is reaching for Isildur, Isuldur takes the hilt of Narsil and cuts all of Sauron's fingers(minus the thumb, I think) off his hand. The absense of the Ring's power causes Sauron to be defeated and to flee his physical form. Then Isildur picks up the finger and removes the ring.

I hope this helped