We have eventually decided to use WINBIOS (an IBM bios display tool)
when you use the /G option it displays the full nine yards of BIOS information, one of the fields (can remember which one - I am at home) is desktop, laptop, notebook etc - this is assuming that the manufacturer took the trouble to set this, but to our surprise - this works with all of our workstations.

However, we already happened to be running winbios on each workstation, so it was no trouble to get this extra piece of info.

FFT
Mark