What other network?
Would that be a Novell network, or a Windows network?
In both cases you can find there is more than just entering a name and password, there is also the server you want to log in to and so on. Even more so on Novell.
Then again, to confuse you even more, there are registry settings in Windows XP pro that can cause the LOCAL login name and password to be automatically set to defaults under certain conditions. Local PC and network identities are not always the same.....
In short, you need more of a leg-up from the previous manager. You will not get access to his data without logging in with his ID OR logging in with full rights, and you cannot create a new user with full rights unless you are a user with full rights already ! Catch-22
You should search MS technical database, because this problem is not exactly rare.