Can not add Domain admin to trusted domain

I created external trust between two Win2000 servers SP4. after creating trust i am unable to add Admin account of Domain A to Domain admin account in Domain B nor i can add Admin account of Domain B to Domain A Domain admin account. i created Secondry DNS zone on both Domains. but when i go to active directory user and computer and try to add admin account of Domian B i can’t see Domain B. i can ping both way by host name as well as by IP. any quick reply will be helpful.

Thanks