To install Europa Barbarorum on your Mac there are two Mac OSX packages available.
It is packaged using the DMG package format, rather than a Widows installer so you can install it on the Mac as you would do with other software.
It requires the Mac OSX version of Rome: Total War (by Feral Interactive) to play.
It bundles EB 1.1 and EB 1.2 together with a few of the fixes released since EB 1.2: it can be considered a 1.3 version of sorts.
This version of the mod differs in several ways from the Windows version: Thanks to the kind work of a Feral Employee, the mod is now available repackaged in a Mac OSX friendly format.