I have the latest 64 bit version of PostgreSQL. I am running Win 7 64 bit. I had installed the ODBC driver (via the initial installer) when I installed PG, and upgraded it to the latest version from http://www.postgresql.org/ftp/odbc/versions/msi/.
However, when I go to the ODBC control panel and try to add a User DSN, PostgreSQL isn't listed as a server.
I was following the instructions given here, but I noted the links are dated.
As I see PostgreSQL installer doesn't include 64 bit version of ODBC driver, which is necessary in your case. Download psqlodbc_09_00_0310-x64.zip and install it instead. I checked that on Win 7 64 bit and PostgreSQL 9.0.4 64 bit and it looks ok:
Test connection: