Assuming that u need to Secure your computer, Completely , i can say 4 things to you :
1. Disable Guest account :
=> goto control panel ( classic mode)>>user accounts.
=> Disable Guest account , if it is enabled.
2. Password Protect your Account:
=>Goto User accounts, click your account. create a strong password.
3. use "USB lock AP" :
"USB lock AP" is a small software that can Password Protect your USB and CDROM, from any unauthorized access .
4. Enable Password in screen saver :
As an additional security, add a password and enable your screen saver. In that way, if you r not in front of your computer for too long, it might prevent others from using your computer.
for more info, do mail me at dhilipsiva@gmail.com or add me to yahoo messenger using dhilipsiva@yahoo.com