Rafael, it is quite easy to run 2 PG versions on the same machine. You need only run one version on the default TCP/IP port of 5432 and installed in the default location such as /usr/local/pgsql(varies by OS); then, install the other version in a different set of directories and use a different TCP/IP port. It is quite easy to configure AOLServer/OpenACS to talk to whichever PG version you wish it to.