I am not sure if this code is up-to-date, I do have a PostgreSQL installation on my Win64, and it is working correctly. Please file a bug report so that the responsible developer can see this issue. But even if it can be fixed, be warned: much of the code is in the FCL, and thus it will take quite some time until is finds its way into an FPC release.
Why don't you build a 32-bit application? I tested it, and Postgres is displayed...