Server 2000 to 2008 migration issues

I am replacing a 2000 DC with a new 2008 DC, no Exchange involved. Ran the adpreps, transfered all FSMO roles, set new as GC, setup DHCP, DNS, and WINS. Unplugged the old DC and now unable to browse network and access to programs on other servers is extremly slow, plug the old one back in everything is fine. I have enabled computer browser and turned on NETBIOS on the new DC, but still get the same results after unplugging the old DC. What am I overlooking?

Also something I have never saw before, all PC's and VOIP phone are set to use DHCP but they always pull the same IP address. What could tell it to get the same IP?

Thanks in advance.