How do you change Service Tag # on Dell Laptop

I too have recently had a warranty MB replacement on a Dell Labreastude D500 with the result that there was no Service Tag information entered into the BIOS and consequently I could not enter any BIOS pbuttwords. Dell phone support did point me to buttet.com but the resulting Service Tag number was only 5 digits long whereas the one on the tag on the computer is 7 digits. Am I not seeing something here? Is there a utility that I can use to put the correct Service Tag in the BIOS? The Dell phone support technician seemed relatively clueless as did the service technician who replaced the board. Also to the person who bought the computer on e-bay and has no proof of purchase: Warning! I recently had a Labreastude D505 stolen (new in box) and expect that it will show up eventually on e-bay. Don't support these theives by buying their merchandise on e-bay and then using legitimate Dell utilities to try and get around the support issues. Sorry, my rant for the day.