Fitting a mixed negative binomial model

Dear list members,

I want to fit a nonlinear mixed model using the nlme command. My dependent
variable takes the form of event counts for different countries over a
number of years, and hence I was going to fit a mixed effects negative
binomial model. The problem, as far as I can glean from Pinheiro & Bates
2000, is that I need a model that is not normal in the errors. All the
models they discuss have linear error structures. Is there a package in the
R language that fits a negative binomial mixed effects model?

Thank you,

Jose Aleman
PhD Candidate
Politics Department
130 Corwin Hall
Princeton, NJ 08544
609.937.0190