Hi Travis,
I have the same Avast! installation setup, you have, at one of my customer site and ADNM, Managed Client (both Server/Workstation) is working fine.
Are you sure the managed computer are listed in your Windows 2003 server Domain Computer list ?
If you are not able to managed the listed computer from this liste (in Windows 2003 server) you have another problem than Avast! itself.
Hope this info will help you solving your problem.