Census coverage

[Dave Hyduke]

Hello,

What's the best way to get external vector files into GRASS raster
so that they can be overlayed?  I want to know the population inside
of a polygon.  I'm starting with ascii counts by tract, the tract
in TIGER boundaries,  and x,y(UTM) for the polygon.  How do you fill
a polygon?  I can probably create the raster files in "C", but is 
there a way using GRASS commands? 

Thank you.