You need to use Unicode which of course supports Perso-Arabic script
http://en.wikipedia.org/wiki/Arabo-Persian_script[
^].
This script is quite popular and probably never been a problem with the Web since Unicode was well established.
Make sure HTTP uses
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
(Be sure to save all your files in UTF-8 encoding, of course :-).)
The font should support the script, of course, but I believe on most modern system it will be supported by default. Even I used to write some Persian for testing purposes (with some help of my Persian-speaking colleague) :-).
—SA