I have been often frustrated by Safari's apparent inability to display Arabic web sites correctly, whereby Arabic words are displayed as single characters without ligatures. It turns out that this behavior has something to do with defective versions of Times New Roman and Arial fonts belonging to Microsoft Office.
According to information on this page, removing these fonts, or replacing them with the original versions installed by OS X, will solve the problem. It worked perfectly for me.
[robg adds: I haven't confirmed this one.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061011095445798