Need to password computer on network

I have a computer running xp pro. It is connected to a wireless router but is not connected wirelessly it is plugged in. I don't have a wireless card for this box yet. Some computers in this house (3) are connected wireless and this one and one other are plugged into the wireless router. I need to password protect this machine over the network. I don't want everybody having access to my files. How do I do that? Sometimes my kids and friends come here and connect to the net wirelessly too and I need to protect my personal data. The only way to have access for some but not others is through passwording. Windows doesn't seem to have this. I have installed sp3 and I thought that had some new stuff on it for this purpose but I can't seem to find it.

net user guest ******* x is the password you choose, the user will have to type in a password to gain access to shared folders. guest account has to be turned off.
If the person has your pass word and logs in that computer the password only has to be typed in once but if the computer is logged off or shut down the password has to be entered again.

if u want to have a password when ppl on the same network want to access ur share files, try this.

goto control panel -> administrative tools -> Local Security Settings -> Local Policies -> User Right Assignment -> Deny access to this computer from the network, then u add group 'Guest' into the value

after set, other ppl want to access ur computer will required a password which is ur windows login password. so Login password is must before u do this setting. try!!