Vector to raster "zone" conversion...

Rsiggeo'ers:

    Given a vector file containing polygons and a raster file of the 
same projection, I would like to create raster "zones" based on the 
polygons -- e.g. I would like to rasterize the vector polygon at the 
resolution of the raster.  I'm not seeing any obvious way to do this -- 
any ideas?  In the end, I want a set of x,y coordinates of all pixels 
which fall within a given polygon -- ideally I'd like donuts to be 
properly rasterized, and some level of control on how much of a pixel 
must fall within a polygon to "count".  I'm trying to port my program 
"starspan" over to R to provide a much needed training/test data import 
capability to complement rgdal and raster's capabilities. 

    Thanks!

--j

Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
One Shields Avenue
The Barn, Room 250N
Davis, CA 95616
Phone: 415-763-5476
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307