Network 'sign-in' settings

[KF4SQB]

OK, here's the deal. I know what I want to do, and I have done it before, so I know it can be done, but I can't remember how I did it. I have a small home network, Windows XP Pro, and I want to change how a user logs into a computer in the network from another computer in the network. Currently, if the computer you are signed in on uses the same username and password as the one you want to 'connect' to is currently logged into locally with, everything works fine. You can access the data on the target computer normally. If, however, you aren't signed in under the same username, it won't let you connect. I've had them configured before so that if you try to access one account on one computer from a different account on a different computer, it simply asks you for a username and password, and gives you full access if you supply the correct one. I would rather it ask for the username and password every time you try to connect, no matter if you are under the same username and password on both systems. If it matters, there is no server in the network (yet), every computer is an 'independant' workstation, and I'm using a 'workgroup', not a 'domain'.