From the link below:
http://answers.yahoo.com/question/index?qid=1006033033807
There are two types of manslaughter and according to the law, both are unplanned.
Voluntary manslaughter or nonnegligent manslaughter, is killing in a heated moment (not planned), and in usually provoked by the victim.
Involuntary manslaughter is the wrongful unplanned killing of another person.
So the only way to "attempt" manslaughter would be if you were in the act of committing a heat of the moment murder and were interrupted or stopped while in the midst of the act. For example: road rage, beating someone with a baseball bat but stopped short of killing that person by a cop or bystander. You were so enraged, you would have killed the person in the heat of the moment but were stopped by others...the intent was there, the completion was not.