ful and trouble
of moving a TCP/IP network
over to a new range
of IP address
Involves router configuration, creating new reverse DNS zone files, overhauling the old DNS zone files, and convincing InterNIC to grok where your nameservers are in the new set of addresses.
Oh, and then you have to actually tell the individual machines what their new addresses are. Unless you're using DHCP, which is a Good Idea.