Hi rexc,
I've never heard of getting the serial number of ANY computer, IBM included, over the network. In fact, I've never been able to get the serial number of a computer using software, even if the computer's sitting in front of me. I know that Dell embeds their service tag numbers (not serial numbers) somehow in their BIOS, but again, you can't read them off the net. You will probably have to go and look at the physical machine (cricking your neck and straining your eyes in the process)...
Good luck,
--Michael