Hi,
I've added a script to the wiki add-ons page to rectify an image using
gdalwarp's thin plate spline method.
use r.in.gdal to load image into simple_xy location
create imagery group, target (i.group, i.target)
use i.points to set GCPs
use i.warp to create a GeoTIFF referenced in the target projection.
(takes raw import file as input, not raster map!)
change to the target location and import with r.in.gdal.
http://grass.gdf-hannover.de/wiki/GRASS_AddOns#Imagery_add-ons
beware bugs in gdalwarp?
http://bugzilla.remotesensing.org/show_bug.cgi?id=864
Hamish