Wirelessly posted (Mozilla/4.0 (compatible; MSIE 4.01; Windows CE; PPC; 240x320))
In ATL (and I assume elsewhere), you can check in either NW or DL flights at the DL kiosk. The first screen has you choose DL or NW. I know if you choose NW, it routes direct to NW's kiosk check in tool. I don't know if you can drop your bags at DL, though.