Cool. I have one more nit-pick though

Rather than modifying the build file to set these paths wouldn't it be better to override the defaults by passing the path as a property to ant on the command line.
Since the build file is in CVS it seems "unclean" to have people make local changes to it.
e.g. we could use
ant -Dopenal.home=blah
Or maybe better, have a property file that can be edited for the system that is not part of CVS but overrides the properties in the build file if present.
ant -propertyfile mydefs.properties
There is also the option of using the ANT_OPTS or ANT_ARGS environment variables.
Like I said - it's a nit pick. I think it will make things a little bit cleaner, but what we have now is working well too.
If there are other paths like this that need to be set for the other core projects (JOGL, JInput) it would be nice to standardize on the method of specifying them. Consistency makes things easier to deal with. Maybe we should be looking at some other projects to see what they do. (unless they say to modify the build.xml

)