Chris,
In case of right to left languages, the recommended option seems to be the ME (Middle Eastern) version of Photoshop or InDesign.
I have no idea about how good is the support for Syriac typographic needs <
http://cg.scs.carleton.ca/~luc/assyrian.html> in that software (that is made and distributed by WinSoft <
http://www.winsoft.fr/winsoft.html>).
I think that in the InDesign Windows <
http://www.adobeforums.com/cgi-bin/webx/.ee6b33c/> forum there are some people (Teus de Jong and some others) that could help you better, as they are used to work with this kind of issues.
Hope it helps
(Posted from Spain)