The dictionary is based on Tim Buckwalters work presented at Qamus. This is a work in progress. Programmers, linguists or users that are interested should feel free to contact the author at email@example.com.
Mac OSX PPC 10.3.9 or above: download.
Windows .NET 2.0: download.
The windows version requires version 2.0 of the .NET runtime available from Microsoft here. In addition you must enable right-to-left language support under Regional and Language settings in the Control Panel.
Users with western keyboards will probably also be interested in arabic keyboard layouts like the one available here.