first, you'll need to open the Passwords icon sitting inside your Control Panel. You'll see the "User Profiles" tab; flip to it and select the "All users of this computer use the same preferences and desktop settings" option. Did that do the trick? Okay, if you still have an active account, change its password. On the "Change Passwords" tab, click the "Change Windows Password" button. Enter your old password and leave the fields for your new password completely blank. If that STILL didn't do the trick (and you'll find out when you reboot), consider taking it up a notch by removing the "PWL" file in your default Windows folder to start fresh; make a backup copy for permanently erasing it. The PWL stores more than the Login account; if you can't remember your screen saver password, this is the culprit. 

There's yet another way to rid yourself of that Login dialog. Right-click on the Network Neighborhood icon and pull up its properties. For "Primary Network Logon," select "Windows Logon." Reboot... and hope you don't see that sucker again.