package for writing shapefiles from SpatialPolygons?
What is a shapefile? It has a *.shp, a *.shx, _and_ a *.dbf at least. So you can't go from a SpatialPolygons object to a shapefile, it has to be SpatialPolygonsDataFrame, even if the only column in the data frame is just a holder. So create a data frame (with row names equal to the Polygons ID values), make a SpatialPolygonsDataFrame, and writePolyShape().
Oh sorry, I had missed that "writePolyShape" function. It's aliased to its read counterpart, and I thought I was seeing write.polylistShape. Thanks!