[R] 2 x 2 Contingency Tables and Type II Error

[Lorenzo Isella]

Dear All,
I am struggling with a the calculation of the type II error (i.e. what  
leads to the statistical power) for a 2 x 2 contingency table.
I see that R can easily accomplish a lot with the chi-square on a  
contingency table

http://bit.ly/VeCrxP

but I do not find an indication for the probability of accepting the null  
hypothesis when it is false.
Am I missing the obvious?
Many thanks

Lorenzo