MS Word for Mac currently cannot do complex scripts such as Arabic or Hindi, and it looks like the next edition, to be released with Office Mac 2011, won't have that capability either. But my initial tests of the Word Web App now available as part of Windows Live Office indicate that these scripts are possible when using this "cloud" version.
A reader with a PC has confirmed that they display correctly when the Word Web app .docx is viewed or downloaded with a Windows machine. Whether such a doc created using a Windows machine will display correctly on a Mac remains to be tested.
There seem to some input problems with Safari when the Alt/Option key is required -- characters may not appear in the text. Firefox works OK, however. Opera does not work at all.