Cannot install pgAgent on Windows

I have PostgreSQL 9.0.1 correctly installed and working for a while. Now, I
am facing the need of getting some tasks running automatically and I thought
about using pgAgent, so, I downloaded version 3.0.0 from
http://www.postgresql.org/ftp/pgadmin3/release/pgagent/ and performed the
following steps:

1. I unzipped the downloaded file. The unzip process created a folder named
pgAgent-3.0.0-win32 and I copied such a folder to c:\Program
Files\PostgreSQL\9.0\pgAdmin III. Now I have c:\Program
Files\PostgreSQL\9.0\pgAdmin III\pgAgent-3.0.0-win32 folder.

2. I ran pgAdmin III, opened the pgagent.sql script and executed it without
trouble.

3. I opened the pgagent_upgrade.sql script and executed it, which displayed
the following message: "column «jstconnstr» already exists in relation
«pga_jobstep»". (I am translating from Spanish to English). Nevertheless, I
decided to continue.

4. I opened a command prompt window and typed the following (as instructed
in pgAdmin III help for pgAgent installation):
INSTALL pgagent -u postgres -p password hostaddr=127.0.0.1 dbname=postgres
user postgres
After hitting the enter key I got a message saying that "INSTALL is not
recognized as an internal or external command, program or batch file".

5. So, I made a change and typed:
pgagent INSTALL -u postgres -p password hostaddr=127.0.0.1 dbname=postgres
user postgres
This time I got a message saying that "Error when starting the application
because LIBPQ.dll was not found. Reinstalling the application may solve the
problem".

As you can see, I am not able to correctly install pgAgent for some reason.
Actually, this installation is being performed in a 32-bit Windows XP
operating system for testing purposes. Finally, it will be running in our
32-bit Windows Server 2008. I use accounts with administrator privileges in
both machines.

I will very much appreciate any help to solve my issue.
The error messages I am getting are in Spanish language and I am translating
them to English.

Respectfully,
Jorge Maldonado