The code below is done in VB Script... It'll pull out the Service Tag and display it in a pop up window. Hope that helps.

Set objWMIservice = GetObject("winmgmts:\\.\root\cimv2")
set colitems = objWMIservice.ExecQuery("Select * from Win32_BIOS",,48)
For each objitem in colitems
Wscript.echo "Dell Service Tag: " & objitem.serialnumber
Next