JDBC driver compilation issues

I am pretty new to Java and certainly the first time trying out
anything with Ant. I work on a proprietary product which distributes
postgres with it and we are upgrading from PostgreSQL 7.2.1 to 8.1.5.
What I found out is that the JDBC source has gone out of the main
distro and is available as a separate source / binary download.

I need to make some customizations to the JDBC driver so I need to
build it from source. I am using Ant 1.4.1 and the JDBC driver source
I have download is postgresql-jdbc-8.1-408.src.tar.gz. I extracted
this into a directory and issued the following command and I get this
as output:

>>>>>> begin snip
[amukherj(at)brh30x86 postgresql-jdbc]$ ant
Buildfile: build.xml

BUILD FAILED

/home/amukherj/product/main/src/extra/pgsql/build/postgresql-jdbc/build.xml:49:
Class org.apache.tools.ant.taskdefs.condition.Or doesn't support the
nested "isset" element.

Total time: 0 seconds
<<<<<< end snip

I don't have much clue into what needs to be fixed but I am getting a
vague idea that the Ant version I am using might not be be able to
build this one.

--
Against stupidity, the very Gods themselves contend in vain --
Friedrich Schiller