Syriac, a major literary language in the Middle East from the 4th to 8th centuries, is not yet included in OS X. In order to read Unicode text in this script you will need to install the BethMardutho fonts. To input Syriac you need to install a keyboard layout found here.
Xenotypetech also sells an excellent Syriac Language Kit.
You will need to deactivate the Damascus Arabic font provided with OS X, because it has a bug which interferes with Syriac fonts.
Here is a test page using the Lord's Prayer. And here is a graphic version of the same text.