Here's a PostgreSQL patch for 4.5.0h.
Here's how to get it installed... First, download and install the postgres (8.2 is the latest currently) server from postgresql.org. Then, download the full Sugar Open Source 4.5.0h (the mysql version, not the one for Microsoft SQL Server) and unzip it in your webserver directory. Next, unzip the attached Sugar-4.5.0h_PGSQLFiles.zip file in the same directory, overwriting the existing files with the ones in the Sugar-4.5.0h_PGSQLFiles.zip file. Then run the installer as usual.
Some issues:
The demo data won't install, so leave that option unchecked.
I had to change many core files due to that Postgres REQUIRES the AS keyword in sql statements when a field is aliased, where in mysql and mssql server it is optional. Sugar is full of queries with aliased fields without the AS keyword, though in many ueries it is already present.. (may I submit a feature request: sql coding standards

) Due to these changes, please be aware that the postgres patch is not upgrade/patch safe.
Disclaimer:
I'm sure there's bugs in there somewhere, let me know if you find any.
I did this port just to familiarize myself with the Sugar code, and I've tested the basic functionality, but that's it...