Password caching

When someone sets up a share in windows sharing, passwords can be
enabled... But when someone enters the password for a share on a
computer, the computer doesn't ask for the password 'till the next
reboot, I don't want the computer to cache the passwords, is there a
way to disable them? (Using Windows XP Home)..

I tried the registry key about caching, I added it (because it wasn't
there) and that doesn't work.. :\

- Ruben