Have you followed the proper procedures for joining a domain? I'm assuming here that you set up the first server as a domain controller and the second server as a member server (stand-alone) that you want to join the domain. Given that, here's MS's info:
Log on to Windows 2000 (on the 2nd server...the "member" server" as an administrator or as a user with administrator rights.
Right-click My Computer, and then click Properties.
Click the Network Identification tab, and then click Properties.
Click Domain, type the name of the domain to which your computer belongs, and then click OK.
If you don't know the domain name, contact your network administrator.
When prompted for Domain Username and Password, type your user name and password, and then click OK. (this username/password has to be an adminstrator's password for the domain controller)
Note If your computer account and user account are located in different domains, you must type the user account domain, followed by a backslash and the user name, in the Domain Username and Password dialog box. For example:
DOMAINNAME\UserName
Click OK when finished. Click OK again.