This procedure may vary depending on the version of MAC OS that you are using but it should be very similar.
1. You will need a Windows 2003 Server up and running as a domain controller.
2. On the Mac, we will need to go into Directory Services which should be in /Applications/Utilities...
3. Click the services tab and you should see a check-box for Active Directory
4. Next, you will have to know your actual domain name and you will have to create a computer name for the Mac.
5.After this is completed, you can also click Show advanced options for additional tweaking but normally, this is not necessary.
6. Once you are satisfied with all of the settings, click the Bind button to connect. You will then be prompted to log into the domain.
7. The last step would be to disable automatic login in order to be prompted for the domain login. This can be done by pathing to System Preferences / Accounts / Login Options, and make sure Automatic Login is disabled.
8. After rebooting, you should be prompted to log onto the domain (domain/username)
9. Also, many claim that Digital Signing of Network Communications must be disable to allow SMB to function properly, but just as many disagree. I would try the above steps first and see how it works out.

Hope this helps,
Paul
NetLock Systems