Afaik it was included in slack 8, but u can download from http://www.postgresql.org,
if u want use it with java u will need also jakarta-ant from http://jakarta.apache.org
According to my reading postgreSql is a real DBMS, it is not as fast as mySql but it has all features ppl expected from a real DBMS (trasaction rollback n few other thing that not implemented by mySql, that y mySql is faster). My conclusion is, if u need a DBMS only for storing web related pages, small time databaser .. mySql might suit better in the point of fast access thinner postgreSql, but if u consider to use ur DBMS for banking process or colaborate with enterprise u will need a real DBMS, postgreSql is one of such, it has gone long process ..
Wut made negative point of postgreSql for me is that if It needs cygwin to run on windows platforms, have to compile it, no binary distribution for windows-platforms. Does it really matter ?