[doug*platypus]

I think we can assume that whatever Saruman's ring did do, or was intended to do, it was not in the end very powerful. Gandalf notices it for the first time, after Saruman has fallen into evil. After lengthy study of ringlore and constant contact with the Palantir, he has finally become influenced by Sauron. Presumably he thinks "yes, a ring, what a good idea!" and makes one for himself, one separate from Sauron's control, for his own selfish purposes. What Saruman's ring does is not as important as the fact that he made it.

The best thread I have been onto here yet talks about the feminine nature of the Rings of Power, about their qualities of Yin balancing the Yang of their male owners (Galadriel is described as having masculine qualities). Sauron commits a great sin and creates a ring for himself, and seemingly increases his power. All the others are made as gifts. Saruman commits the same act as Sauron, but doesn't appear to gain anything from it. In the end he appears to be less wise than Gandalf and less powerful than Sauron, and caught in a very dangerous predicament.