Like you I did fresh install of altiris 7
I deployed a batch file via software delivery from my NS 6 setup:
cd "%ProgramFiles%\Altiris\Altiris Agent"
AeXAgentUtil.exe /uninstallagents
AeXagentUtil.exe /server:yourserver
MsiExec.exe /X{4A702DA1-9E48-4346-8030-26B399CCFA8C} /qn
MsiExec.exe /X{332454D8-73B0-4b4a-954C-D96089CD898A} /qn
The msi removes are for Application Metering and Carbon Copy can't remember which why around.
Ensure you have the Symantec Management Agent upgarde policy enabled on your new server.
This worked really well me, you can bring workstations on as fast or as slow as you want.
Darren