KMS Hosts

Hello all,

What does KMS server use as the basis for identifying individual vista
clients? Is it the MAC address on the client NIC, the processor ID, the
motherboard ID, or something else or some combination?

I have Windows 2003 KMS with DDNS enabled. All our clients are DHCP enabled
and I am interested in how licensing will behave if we swap out a Vista PC,
replace it with another one and later swap the original back in somewhere
else.

Thanks