[R] sampling question

[Kirsten Beyer]

I am interested in locating a script to implement a sampling scheme
that would basically make it more likely that a particular observation
is chosen based on a weight associated with the observation.  I am
trying to select a sample of ~30 census blocks from each ZIP code area
based on the proportion of women in a ZCTA living in a particular
block.  I want to make it more likely that a block will be chosen if
the proportion of women in a patient's age group in a particular block
is high. Any ideas are appreciated!