pgcrypto module for WINDOWS

Hello,

We are interested in installing the pgcrypto module of PostgreSQL for
Windows,
In order to use the function digest() for creating index on bytea type
fields:

create unique index my_index on my_table (digest(my_bytea_field, 'md5'));

HOW CAN WE INSTALL THE PGCRYPTO MODULE FOR WINDOWS?
DO WE HAVE JUST TO INSTALL, OR DO WE NEED TO RECOMPILE SOMETHING?
In the first case (just install), what do we have to install and where do we
have to download it from?
In the second case (recompile), what and how do we have to recompile and
where do we have
to download it from?
We have found the library pgcrypto.dell in our hard disk, and also the files
pgcrypto.sql and pgcrypto.readme. We have
read the pgcrypto.readme, but we are made a mistake.

Who needs to know the digest() function, the server or the client?

Bye and thanks for your help.