The driver is available from the files section of the AOLserver SourceForge site -- http://prdownloads.sourceforge.net/aolserver/nspostgres-3.5beta1.tar.gz?download
is a direct link.
This driver is working well for me on an OpenACS CVS HEAD installation.
If no major problems are found in two weeks, this beta will be promoted to full release 3.5.
Many thanks to Scott Goodwin in this release.