determination of voltaic cell voltage if i understood this correctly, the determination of voltage for a specific voltaic (gallvanic) cell is determined only by the chemical correlation between the two metals. is this true? 
for an example , if i use iron instead of zinc in the example from wikipedia, i will get a different voltage?
 A: 
for an example , if i use iron instead
  of zinc in the example from wikipedia,
  i will get a different voltage?

Yes.

is determined only by the chemical
  correlation between the two metals. is
  this true?

No. 
The voltage of a galvanic cell is the sum of the voltages of the "half cells", 
wich can (not must!) be made from a metal and a solution around that "electrode". 
Both the metal (or what else is there as "active" material) and the solutions ("electrolyte")
quality and concentration determine the voltage of this "electrode".
There are cases, in which there is a single electrolyte for both "electrodes" and 
where the influence of the electrolyte on both electrodes cancel out. 
(Eg the oldfashioned acid Zink/Manganese dioxide "dry" cells and the more recent 
"alkaline" Zink/mangese dioxide cells, both have about 1.5 Volts). But in general, 
all components have an influence. 
PS
Be aware that the popular use of "electrodes" (up to physics textbooks!) is wrong. 
The carbon rod in a Zink/"carbon" cell is not an electrode at all. This is a contact 
material able to withstand the corrosive environment. The electrode is a mass of manganese dioxide.  The latter then is "explained" as "depolarisator", a theory obsolete 
(and known to be wrong) since Nernsts law was published more than 100 years ago. 
