I'm not positive if you are looking for multiple task assignments or the ability to have multiple tasks.
If you are looking for multiple responses or "tasks" in one Dialog model, you can click the "Allow Multiple Responses" checkbox in the Interaction Setup tab of the Dialog Workflow and then click Add in the Dialog Models section to add additional tasks.
When you edit those additional Dialog models, you can uncheck the "Exit Component On End" checkbox to keep the task active if it might need to be repeated. Each of the Dialog Models added can have their own dialog model setup, independent of the main Dialog Model for the Dialog Workflow. The following image is an example of how I have one setup:
Doing this introduces new ResponsePageLink and ResponsePageURL variables you can expose for your different task links. The following image shows how I expose those separate task links inside of an Altiris Helpdesk 6.x ticket comment:
Hope that helps with what you are trying to do. If you're looking at doing multiple task assignments, what Rob pointed out on the previous post is the way to go.