I know some people diagnozed with dissociative identity disorder via internet, and what I could say - they are absolutely conscious that they have this disorder. If a person has alters (i.e. multiple personalities), it doesn't necessarily mean that they are not in control of their actions. If their disorder is in a bad state, they usually lose time (i.e. have blackouts), when someone else of their alters are "out" - having the control of the body - and the one who loses time is hiding inside. But usually with time and therapy a person with dissociative identity disorder loses time less and less, and develops co-consciousness with the other alters/personalities in hir body.
I must emphasize though that I am in no way any expert in this area - I only have mild personal experience with alters, as currently I have a teenage alter called Linda in me. I guess my right diagnosis might be DDNOS... I learned about Linda's existence during mentally very rough time in my past - at that time I lost some time, but nowadays blackouts don't happen anymore.
The only thing that gives me distress nowadays is the sad fact that our co-consciousness is very vague, and thus I can reach Linda only occasionally, when really trying to make contact with her. Most of the time Linda is just hiding inside me, and I do not have a contact with her.
I guess my medication (Zyprexa) has something to do with this thingy, and that's why I'm currently switching my med to Risperdal. Let's see what will happen when my body has become used to this new med - I hope to be able to befriend with the Linda aspect of myself better, cuz I'm aware she is the one in me who has the most passion toward my hobbies and life in general.
But what I wanted to say, I don't hear voices while I'm in contact with Linda - rather I feel emotions and/or thoughts that are hers, not mine. However, some people with DID do hear voices while communicating with their alters (if I have understood them right). But - I think dissociative identity disorder is an altogether different mental condition that schizophrenia. I have an impression that a person who is schizophrenic doesn't think the voices as messages from hir alters, but rather s/he gives too much power to hir hallucinations (e.g. voices) - thinking they are special messages from universe for example. So while a schizophrenic person is having a psychotic break, s/he doesn't know s/he's psychotic, but rather s/he believes in hir delusions and thinks s/he is mentally OK.
That's why I think you may feel at ease with yourself, nobody becomes schizophrenic just by fearing that. Please keep in mind what maria said to you in this thread, I think she is right. By the way, there are also people who hear voices, but still enjoy perfect mental health - thus hearing voices only doesn't mean one is going to be psychotic or has alters. All in all, I still must emphazise that I am far from expert - so if there's someone who'd like to correct my assumptions toward schizophrenic states of mind, please feel free to do that...