confidences and probability

I am trying to feed RapidMiner output (predictions and probabilities)  into an external program. I understand how to output confidence scores using ExampleSetWriter, but not probabilities. I found a thread in the old SourceForge forum that suggests using PlattScaling to convert confidence scores to probabilities. I looked around a little bit, but could not get this operator to get what I want. How should I go about doing this? How do I find and write the probability that a particular instance belongs to a class?

Thanks,
B