Fzs1000 is the gen 1 (to 2005) with carbs and steel frame.
Fz1 is the later one with injection, usd forks etc. The S and N means fairing or not, respectively.
Confusingly the gen 1 Thou was also known as FZ1 in the USA. However the gen 1 and 2 bikes look totally different from each other so not that confusing. Hope that helps.