dynamic wf AND task

System

Hi All,
I am working on dynamic workflow and i need to activate 2 task on action with User task- for e.g.
link_tasks(task1(cgitask),task2(externaltask),"comments");
This task2 will have to activate 2 tasks namely, task3(usertask) and task4(dummytask).
link_tasks(task4,task5(externaltask),"comments");
task3 can again call task1 or task5
How can i activate task3 and task4 after task2 in dynamic?

Thanks in advance