Bayesian data mining

Hi, I need a help to know whether I can perform the following in R:
I have a set of observations (Ns) and each observation is drawn from a 
poisson distribution with an unkown mean, lambda. The set of lambdas in 
their turn are drawn from a common prior distribution which is supposed to 
be a a mixture of two gamma distributions.
Is there a way to determine the poisson means in R, given the Ns and the 
probabilities?
And how can one determine the two alphas and the two betas of the gamma 
mixtures? I am assuming there will be an MLE somewhere.
This is to help me understand and apply William DuMouchel concept of 
datamining especially in his article: "Bayesian data mining in large 
frequency tables". Thanks