Forgotten PostgreSQL Windows password

This morning I’ve been trying to connect the Postgresql database on my Windows 7 professional desktop.

The default value is ‘postgres’, but sure enough I forgot what password I used when I originally installed it.

I have googled and found a post related to reset your password-

http://www.postgresql.org/message-id/6BCB9D8A16AC4241919521715F4D8BCE476A42@algol.sollentuna.se

I followed the same. but the end result is a bit different then mentioned in the post.

I have used-

net user postgres postgres

to reset the password for my database but instead of a success message I am getting :

"System error 5 has occurred. Access is denied."

system error. Please guide me if I have missed or approaching wrong to get the end result.
Any help will be really appreciated.

Thanks!