This extract from the Win98 resource kit documentation:
"Windows 98 provides a single unified logon prompt that allows the user to log on to all networks and Windows 98 at the same time. The first time a user starts Windows 98, there are separate logon prompts for each network, as well as one for Windows 98. If these passwords are made identical, the system logon prompt for Windows 98 is not displayed again."
It's called password caching.
Here is how the Resource Kit describes how to turn in on manually. To turn it off, reverse the process described.
"To set up password caching of network passwords
1. In Control Panel, double-click Network.
2. In Primary Network Logon, select Windows Logon, and then click OK.
3. In Control Panel, double-click Passwords, click Change Windows Password, and then click OK.
4. Make your Windows password blank, and then click OK two times.
5. Restart your computer.
6. When asked for a password to log on to Windows 98, enter a password, and then press OK.
7. For each network prompt, enter your network password and make sure the check box for Save this password in your password list is selected."
Remember this is to turn caching on so "do not save password" in step 7 is what you are after
Hope it helps
-Hugh