Found this possibly related post from a postgres forum. Wednesday, March 26, 2008 32 Bit ODBC Drivers in Vista 64
This post isn't really PostgreSQL specific. It also happens with MySQL and Ingres (and any other 32 bit driver).
I am running Vista 64 on one of my machines. I installed Postgres 8.3 and the ODBC drivers. When I tried to setup an ODBC connection, the windows ODBC administrator program ODBCAD32.exe did not list Postgres. I noticed that it also did not list MySQL or Ingres even though I knew I had installed drivers for those databases also.
After a bit of research, I tracked down the issue. My ODBC drivers did in fact install. Microsoft, in all their wisdom, has 2 versions of odbcad32. A 32 bit and a 64 bit. They are both named odbcad32.exe.
It gets better. They put the 32 bit odbcad32.exe in the syswow64 directory. They put the 64 bit odbcad32.exe in the system32 directory. 32 bit apps will pick up the 32 bit registry setting and 64 bit will pick up the 64 bit registry setting. system32 comes before syswow64 in the system path so the 64bit software runs before the 32 bit software.
So, when I manually ran odbcad32.exe in the syswow64 directory, I was able to configure my connections and everything worked hunky dory. I know have a shortcut to syswow64\odbcad32.exe on my desktop for working with 32 bit databases.
I wonder how stable the system would be if syswow64 was in the path before system32? I don't plan to find out.