Bipolar is different to PTSD, in that it used to be a mood disorder, however;, is now a bridged disorder of its own category between depressive disorders and schizophrenia spectrums. Bipolar is often misdiagnosed by physicians in lieu of PTSD, though not normally the other way around, nor normally by people experienced in PTSD.
You can read about latest PTSD dx at: Link Removed
The main difference between bipolar I & II is that for II you have had one major depressive episode and at least one hypomanic episode.
The primary difference between PTSD and Bipolar is whether you have a range of symptoms to meet PTSD, OR, whether your primary issues are all mood based, with or without anxiety.
PTSD is all about anxiety as the primary symptom. Bipolar is all about mood as the primary symptom. PTSD you need a trauma, Bipolar you don't, though one typically exists to create Bipolar.
The two can be very difficult to isolate and it is important to know whether you had Bipolar tendencies prior to trauma, or whether they appeared after trauma. If after, then PTSD is the most likely cause of the symptoms which can reflect Bipolar, though if you had such prior too, then you could actually have Bipolar which is being masked as PTSD, or you could have both.