Hi Michael,
No worries at all, but you've asked a question that requires two answers:
1. The Workgroup setting can now be found on the WINS tab of the appropriate Network service, in the Network system preference. Just select the appropriate service in the list, then click the Advanced button at the bottom-right corner of the window.
2. The Directory Access utility has been significantly changed in functionality. However, it's name remains similar: it's now called "Directory Utility", and it can be found in /Applications/Utilities/. Note that its functionality should not be applicable to your situation here, if all you are trying to do is to provide your Mac with the name of the appropriate Windows Workgroup.
I hope this helps! 🙂
Best wishes to you,
MBJ