A recent project had me trying to script the retrieval of the Dell Service Tag. Luckily there's WMI Command-line to the rescue.
From a command line or in a script wmic bios get serialnumber will display or grab the Dell Service Tag.
Furthermore, you can use the WMI Command-line to retrieve all kinds of system data and even make configuration changes. Rob van der Woude's great site on scripting has a great primer and examples on using WMIC. TechNet Magazine also has a very useful article on gathering system data using WMIC in your environment.
Finally, checkout the WMI Admin Tools pack. It contains more than I want to type about here, but it gives you the ability to browse the various objects, classes and properties, plus a custom event viewer and much more. Check it out and make your (administrative) life better.