How to write Persian/Arabic text in a LaTeX document which is mainly written in English?

Actually, I want to add some sentences in Arabic script inside my PhD thesis. Will it be possible just by adding some \usepackage statement in the preamble or need more than this? This is a bit tricky requirement in the sense that English script is written from left to right but the Persian/Arabic text is written other way around! I don't know how LaTeX deals with such requirements. Any idea?

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 Please have a look at this it includes an example tex.stackexchange.com/a/12406/963. – Yiannis Lazarides Mar 12 '12 at 12:52

You can try the ArabTeX package:
 Thank you for the response. I tried this but it changes the whole document into Arabic text. How to avoid this from happening? How to make sure that only desired sentences appear in Arabic text? – Shah Mar 12 '12 at 12:54 Use \begin{RLtext}salAm\end{RLtext} to get a whole paragraph, or This is a greeting: \ in running text. – LianTze Lim Mar 12 '12 at 13:15 It worked! Thank you very much for your help. – Shah Mar 12 '12 at 13:45 The Persian that ArabTeX provides is useless! – Vafa Khalighi Jun 21 '12 at 3:01