the term "istan", from who does it originate?

hmmm when did the Arabs arabized pul?

its the persian who lost their P .

anyway i think the Istana as Cyrus mentioned is the correct theory for Istanbul's name.

You are wrong, in almost all Ottoman official documents "Istanbul" has been called "Istana/Astana" (it means capital/city in Persian language, the new capital of Kazakhstan is also called Astana).

just read these ones: http://www.gzastorm.i12.com/islam/index.html

I have said it many times and I know you just love to play with words and ignore all Persian sources, anyway I say again that from early times Persians called "Constantinople" as "Istan Bul" which means "Land Bridge", as they said "AfghanIstan" (Land of Afghans) and "Kabul" (Mountain Bridge).

The most common theory is that Istanbul developed from the greek �eis ten poli� (pron: is tin boli)meaning to or in the city. It's likely to have been so, at least linguistically speaking. Culturally, it also makes sense, since Constantinople was referred to simply as i Poli, the City, among greeks, even nowadays. 

I read somewhere that a contraction of Konstantinopouli to Konstanpouli and then simply to Stanpouli (pro: stanbuli) could be also another reasonable explanation.

If in regard to Istanbul, there are several theories but the one mostly maintained is that it's a Turkish contraction of the Greek "est an polis" (or similar) meaning "into the city" which is what the Byzantines were supposedly saying when the Ottomans were close to enter Constantinople.  

Ma`salam