Here are some definitions:

Dissociation is a psychological state or condition in which certain thoughts, emotions, sensations, or memories are separated from the rest of the psyche. For this reason, it is sometimes referred to as "splitting." (Wikipedia, February 2007)

Psychosis (not to be confused with psychopathy) is a generic psychiatric term for a mental state in which thought and perception are severely impaired. Persons experiencing a psychotic episode may experience hallucinations, hold delusional beliefs (e.g., grandiose or paranoid delusions), demonstrate personality changes and exhibit disorganized thinking (see thought disorder). (Wikipedia, February 2007)

Dissociation: In psychology and psychiatry, a perceived detachment of the mind from the emotional state or even from the body. Dissociation is characterized by a sense of the world as a dreamlike or unreal place and may be accompanied by poor memory of the specific events, which in severe form is known as dissociative amnesia. (http://www.medterms.com/script/main/...ticlekey=38857)

Psychosis Definition: Psychosis is a loss of contact with reality, typically including delusions (false ideas about what is taking place or who one is) and hallucinations (seeing or hearing things which aren't there). (http://www.healthscout.com/ency/1/001553.html)

Based on that, alone either of those experiences are not the same. They are part of seperate groups under the DSM-IV, as dissociative disorders and Psychotic disorders. That's not to say people with a psychotic disorder don't experience dissociation or vice versa, but as a singular meaning/experience they are different.