2 ways to use a specific task list for your workflow:
- create a new task list with a name which makes the new task list the "first" task list available. After the workflow is associated with this new task list, then you can go ahead rename the task list to your liking.
- modify the *.wfconfig.xml in SharePoint Designer. Specifically, change the TaskListID to the tasklist id of the task list you want the workflow to use.