Well today I had to connect to one of my client's servers and download the Dell Raid Storage Management tool for the machine to check something in the RAID config. I couldn't remember the Dell model number nor retrieve the service tag. In the end I used the PowerShell and WMI to retrieve the service tag:
in Windows PowerShell execute the following cmdlet:
Amongst other BIOS info, the cmdlet returns the serial number. The serial number Dell program into the BIOS is the system service tag :)
I could then go onto the Dell support site, enter the service tag and go straight to the relevant downloads for the server I was dealing with.