I guess you've wrong Character Encoding settings in your browser.
Check the following:
1 - Make sure your language is supported in the Regional settings [Control Panel-->Regional Settings -->Language Tab, check both Support Complex Scripts, and Support/Install Eastern Languages] The last option may require Windows CD and Reboot.
2 - In your Explorer/Browser (e.g. Internet Explorer, Mozilla Fire Fox, ...) open your page (your Hotmail, Arabic subject), select View menu--> Character Encoding--> Arabic (Windows-1256) or Unicode (UTF-8). Such encoding are usually used in many Arabic pages and web page designers sometimes forget to set the default encoding in their page (<meta...> Tag).
That's what I guess and hope it will solve your problem, good luck.