Converting Spatial Polygons to data frame for krige.conv

do you want the coordinates of all the vertices of your polygons?
Have a look at ?geometry. But this doesn't take you down to a mere list of coordinates. There might be a more elegant way, but you can try that little function to achieve this:

   asText.SpatialPolygonsDataFrame <- function(obj){
       coords <- matrix(double(), ncol=3)
       for (Polygons in obj at polygons){
           for (Polygon in Polygons at Polygons){
               coords <- rbind(coords,
                   cbind(as.integer(Polygons at ID), Polygon at coords),
                   c(as.integer(Polygons at ID), NA, NA))
               }
           }
       return(coords)
       }