Solução:
//Create new columns
proj.TaskTables[proj.Index].TableFields.Add(MSProject.
PjField.pjTaskText1, MSProject.PjAlignment.pjLeft, 15, "nome coluna 1", MSProject.PjAlignment.pjCenter, 2, true);
proj.TaskTables[proj.Index].TableFields.Add(MSProject.
PjField.pjTaskText2, MSProject.PjAlignment.pjLeft, 15, "nome coluna 2", MSProject.PjAlignment.pjCenter, 3, true);
Aline Mayr