9.1 is not supported yet - early tests suggest that there are still problems with it.
However, that may not be your problem here. If you installed it yourself then you would have set the password manually so you will need to use whatever password you specified. Alternatively you can remove the need for PostgreSQL passwords:
How To: Remove PostgreSQL Password.
However, if PT3 can't connect at all it could also indicate that the PostgreSQL service isn't running - sometimes security software can interfere so please check our
Firewall Guide too.