how to disallow others to log on to a shared computer?

Answer 1

You don't say what operating system you are using, so I'll assume for the moment that you're using Windows XP.

Windows XP has the feature of setting up separate profiles for each user. You can find this area in the Control Panel. (Start- Settings - Control Panel) The icon is labeled User Accounts.

When you first call up this area, you will see a link which says "Creat User Account". Give the account a name (it can be something easy like "Mary" or "Joe" or something more direct such as "User01".
Click Next.
Now you can specify the amount of power you can give this user. Administrators can install programs and control such things as other peoples accounts and passwords. For more security, always start someone with a Limited setting.
Click Create Account.
Now Click on the New account Icon.
Click Create Password.
Enter a password (always good to use both letters AND numbers for a more secure password) Click Change Password.

It's that easy. You can create a different account for each user you want to have access so that users will not have to share accounts.

Answer 2

while sharing a folder there is an option wherein the shared folder can only be viewed by the people you want.
Right click on the shared folder and go to sharing. in this click on permissions and enter the name of the pcs who should view the folder.

Answer 3

Setup separate accounts. Password protect your documents.