The Arial Unicode MS reference article from the English Wikipedia on 24-Jul-2004
(provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Arial Unicode MS

For people who check facts
In digital typography, Microsoft's Arial Unicode MS OpenType font is designed to support all characters defined in the Unicode standard, version 2.0, including support for most previous Microsoft code pages. It is a variant of Microsoft's Arial font.

It was previously available for download, but now is only distributed along with Microsoft Office. It contains support for most Unicode ranges but certainly not all of them.

Other well-known Unicode fonts include Code2000, Lucida Sans Unicode, and the Free Software Foundation fonts.