To make sure as many of your Task Agents as possible attach to the new Task Server you need to set up your sites and subnets as laid out here:
"Best Practice: Managing Task Server Communications in 7.0 and 7.1"
http://www.symantec.com/docs/HOWTO48411
Another way of seeing how many Task Agents are on each Task Server is to look at the built in Filters under Manage > Filters > Computer Filters > Task Service Filters.
I run a "Reset Task Agent" task daily at 10:00 am on all Task Agents in the Filter with Task Agents reporting to the NS.