You can easily add a password to your user account to keep unwanted people out of your computer.
To add a password in Windows XP or Windows Vista do the following:
Click on start then control panel, make sure you are in classic view (upper left corner), then click on user accounts and click on add/change your password.
Make sure when choosing a password for online accounts and computer accounts… you use a unique password that is hard to guess. Use a password that contains letters, numbers and symbols when possible. Most websites will require you now to use different characters when choosing a password. Also try to come up with one you will use all the time so you will not forget it but make sure its long enough to cover some website guidelines on length.
Example: 308*Abc$