"Two DHCP servers on the same subnet is only for the gurus,"
had exactly that situation this morning on a small site which had just been upgraded from XP to Win7, involving new machines and servers
We couldn't twig why the internet kept collapsing, yet the web-based business software was OK
Several hours before someone twigged that the old server was still on the network and trying to route DHCP requests....
Doh! Serious Homer Simpson moment......