What OS are you using?
If you are using XP, then I would set up your confidential files in a separate user account. With XP you can set up various guest/user accounts, with or without administration privilages.
Goto user accounts and setup another account, transfer your important stuff into that account and password that whole account. You can then simply choose to log onto that account at the welcome screen, or the switch user tab in the start menu and jump between the 2 accounts as and when you need too.
Then you can use your computer normally, knowing your documents are saved in another account within the computer.
Tip - Always backup your data, no matter how unimportant you may feel it is, cause sure as fate, it will come back to haunt you if you don't.
I have only used XP, so I can only give advice on that OS...but if I were you, I would set up a whole new extra account and password it. Maybe dont give it admin privilages either for extra security.
Hope that helps in some way.