Changing the error structure in SPSS


I need to change the error structure in an analysis of count data to poisson. I have one fixed factor (2 level) and one covariate. The data is not normally distributed and all transformations I have tried (ln(N+1) or SQRT(N)) could not normalise the data. The variance is homogenous though. As I said I would like to change the error structure to poisson but don't know how.

Can anyone help?

Many thanks.