I am sorry to repeat it, but I do not know if you see my comment because of the comments pagination. I told you that:
I think you are missing one step. Once
you see that little red X, you have to
click on this postgres icon. Then, you
should be prompted with the user
(postgres) and the password you
specified during the installation.
I hope it helps you. Regards.
The red cross means that you are not logged. If you have seen my previous comment and this does not solve your problem, please, tell us what happen exactly when you click in the icon with the little. red cross.
Another thing you can try is to login from the console. To do so, load the enviroment:
And try running the psql command:
psql -U postgres
You should be prompted with the password you used during the installation.