Peer to peer network and account names

i've a problem trying to rename some accounts in a peer to peer lan.
I have a computer that shares some folders and in which i created from
control panel- user account usernames and passwords for all the users of
the net. everithing works right.
If i change the user account name in a pc of the lan and i change it
also in the "server" pc when i try to access to the server from network
neighborhood it asks me username and password.
How can i fix it?

Sorry for my poor english!

Vera