Stein: no, you can't password-protect with client-side scripts or markup. Any code you wrote would have to be interpreted by the browser, which means it is sent to the browser, which means any password would be embedded in the code. It's as simple as viewing the source, then entering the password.

Encrypted Password Generator
Use our password generator to help password protect your web pages. Using advanced JavaScript techniques and some ciphering tricks, this program encrypts the password specified before storing it on the page, making it "unviewable" by simply looking at the page's source.