You actually don't have to wait for Dell to release a slipstreamed Vista SP1 disk to get one working with all of the auto-activation and Dell OEM stuff.
Just copy the PID.TXT file from the /sources folder to a temp folder. Also copy the entire $OEM$ folder from the /sources folder into the same temp folder.
Find a torrent for the Vista SP1 "MSDN" disk, download it, extract it to a folder, and put the $OEM$ and PID.TXT files into the /sources folder of the new directory with the Vista SP1 "MSDN" disk you extracted.
Make a bootable DVD image with vLite, burn it, and you have yourself a slipstreamed, Dell OEM Vista SP1 disk.