Calculating Weighted Income Quintiles for PUMS Households in R

Hi Folks, 

I'm interested in creating a dummy value in R to identify which income quintile a household is in using PUMS data. However, I'm not sure what the code should look like. I'm guessing that I need to get the number of households at each income - so weighting the households and grouping them by income. Then, I have to calculate the quintile breakdown, and create a (1,2,3...) dummy variable to use in further analysis. 

But I'm somewhat at a loss as to what that might look like - in particular, whether or not there is a quintile calculation function for R.

Anybody have a sense of what that code might look like / where to start looking?