Dell Service Tag

If you have Dell servers, and the service tag isn't set in BIOS for whatever reason (motherboard replacement and etc), you can use this tool to update the service tag.

Found this post in the Dell community forum on how to do this:

http://en.community.dell.com/support-forums/servers/f/956/p/19101767/19226362.aspx

You can use the Asset tag utility to do this. There are hidden switches to asset.com to change the service tag.
ASSET.com version 2.09 from the resource CD would be the likely candidate.

ASSET 209 Asset Version 2.09
Release Title: System Utilities:
Dell Asset Utility, Utility, English, Multi System, 2.09
Release Date: 09/27/2005
Description: Asset Utility
http://support.dell.com/support/downloads/download.aspx?c=us&cs=19&l=en&s=dhs&releaseid=R109071&formatcnt=1&fileid=141647

boot from dell resource CD
choose "Q" to quit the diagnostics and go to command prompt
navigate to "asset209.exe" tools
cd csd\tools\bios
run "asset209.com"

Usage:
ASSET new_asset_tag Specify new asset tag
ASSET /d Delete asset tag
ASSET /o new_owner_tag Specify new owner tag (if applicable)
ASSET /o /d Delete owner tag (if applicable)
ASSET /? This help screen

Hidden Options:
ASSET /s new_service_tag Specify new service tag
ASSET /s /d Delete service tag
ASSET /b Specify new system board tag
system board tag must be "ssssssssssssssssssss-vvv-", where
s..s is the 20 digit system board Part number string,
vvv is the 3 digit system board rev,
- is a don't care character, but must be present
ASSET /b /d Delete system board tag
ASSET /f [other_options] Force Affirmative response
ASSET /x [other options] eXtended display - displays all tags

Another Option would be the DCCU:
Release Title: System Utilities:
Dell Client Configuration, Utility, Windows 2000, Windows XP, English, v.1.1.111.0, A00
Release Date: 02/13/2004
Description: The Dell Client Configuration Utility (DCCU)
is a tool for managing Dell clients through BIOS updating,
shutdown/restart, asset/inventory reporting, and SMBIOS,
CMOS and OS parameter setting.

http://support.dell.com/support/edocs/software/smdccu/

ftp://ftp.dell.com/utility/R73202.EXE

http://www.dell.com/downloads/global/solutions/dccu_infobrief.pdf

UPDATE:

It looks like the tool is also available in the "Dell 32 Bit Diagnostics" kit: http://support.us.dell.com/support/downloads/format.aspx?releaseid=R247886&c=us&l=en&cs=19&s=dhs

You can find it in the driver download page for your specific model. Get the non-GUI version.

You create a boot media (floppy, USB key, CD..) with that tool, and you boot the server with it. Once booted you select #4 on the menu, which will drop you off into a DOS environment.

Navigate to c:\util (at least thats where it is for USB boot media), and asset.com is in there. Just use the switches above to do whatever you want.