I would sugest you greatly simplify your life by downloading WinCVS (if you are using Windows) or some other CVS client and abandon the integrated version in eclipse.
Secondly, the username is "anonymous" and the password is "" (i.e. blank). The repository would be "/cvsroot/hibernate" and the host is "cvs.hibernate.sourceforge.net". You can copy all this information off the wiki including the whole connect string, I suggest you read that page first.
Here is the whole connect string anyway:
:pserver:
[email protected]:/cvsroot/hibernate