problems w/ migrated xp's in new 2003 domain.

we just migrated from a 2000 domain to a 2003sbs domain. the 2 servers were put on the same network with different domain names. ie brame.local and bramearchitects.lan. at the time i was setting up the server i did not know that the netbios name for the domains were the same (brame). we had an awful time getting the computers to join the domain, but we did get all of them joined finally. this is an environment with 2000 and xp machines. after removing the old dc, all of the 2000 machines are happy, but the xp's take about 3-5 min to log in. i know this is a dns issue. i have hard coded in the tcp/ip properties of the workstations the dns for the new dc. i have dhcp running from server handing out the ip for dns to server also. in dns on new server i have created a forward lookup zone called brame, which is in addition to the one created automatically during ad setup. the reverse lookup zone has also been created. i think my problem lies in the dns zone that was created automatically. all workstations look to dc which forwards to isp dns. can i kill the auto created zone (it is the mcdcs zone) and just use the forward lookup zone that i created without major reprocussions?? also this environment was using microsoft mail which is now exchange 2k3 (patched up) for internal and pop3 for external. the 2k machines can send/receive internally no problem. the xp's cannot. they can open their mailboxes fine, but if they try to send a message from global address list it gets sent to pop3 smtp which kicks it back.  out bound mail is disabled on the exchange.  any help would be appreciated......thanks