Here are some updated links to help you locate the tool. Best bet would be either the Windows XP SP2 Tools update or the Server 2003 version. The link listed by Les does have the NETDOM.EXE file inside along with a whitepaper, but is an older version then the 2003 and XP SP2 version updates.

Description of Netdom.exe Syntax and Versions
http://support.microsoft.com/default.aspx?scid=kb;en-us;329721

Windows XP Service Pack 2 Support Tools
http://www.microsoft.com/downloads/details.aspx?FamilyID=49ae8576-9bb9-4126-9761-ba8011fabf38&displaylang=en&Hash=W6YFBY9

The following Support Tools have been updated in Service Pack 2:

bitsadmin.exe
extract.exe
httpcfg.exe
iadstools.dll
ipseccmd.exe
netdom.exe
replmon.exe

How To Use the Netdom.exe Utility to Rename a Computer in Windows Server 2003
http://support.microsoft.com/default.aspx?scid=kb;en-us;325354

This article describes how to use the Netdom.exe utility (included in Windows Server 2003 Support Tools) to rename a computer that is a member of a Microsoft Windows 2000 or Windows Server 2003 domain. This procedure can be performed either locally or remotely on the computer that is being renamed. Also, the procedure does not require that you to reset or manually re-create the computer account in the domain.
The Netdom.exe utility can rename a computer that is a member of a Windows Server 2003 domain. However, to rename the computer, you must specify the user accounts that have local administrative permissions and the object of the computer account in Active Directory.

How To Use the Netdom.exe Utility to Rename a Computer in Windows XP
http://support.microsoft.com/kb/298593/EN-US/

Windows Server 2003 Administration Tools Pack
The Windows Server 2003 Administration Tools Pack (Adminpak.msi) provides server management tools that allow administrators to remotely manage Windows 2000 Servers and Windows Server 2003 family servers. This is the final version (build 3790) of the Adminpak.msi file.
http://www.microsoft.com/downloads/details.aspx?FamilyID=c16ae515-c8f4-47ef-a1e4-a8dcbacff8e3&DisplayLang=en

Windows Server 2003 Resource Kit Tools
The Windows Server 2003 Resource Kit Tools are a set of software tools for administrators, developers, and power users to manage Active Directory, Group Policy, TCP/IP Networks, Registry, Security, Scalability and many other areas of the Windows Server 2003 operating system.
http://www.microsoft.com/downloads/details.aspx?FamilyID=9d467a69-57ff-4ae7-96ee-b18c4790cffd&displaylang=en