Windows offers the ability to save passwords for web sites and network resources. This can be very convenient as opposed to remembering and entering the username and password each time you need access. If like I have just had you need to remove one of them then this snippet of information will help you.
get to a command prompt and type in the following rundll32.exe keymgr.dll, KRShowKeyMgr
You should then be presented with a list of your stored passwords
you can edit them and you can delete them