Nice Javascript-Based Form Validation Script

This one is from the O'Reilly site so it must be good. Full length tutorial explaining the different parts of the script. Includes the following functions:

checkPassword()
checkEmail()
checkPhone()
isDifferent()
checkRadio()
checkDropdown()

...among others. Uses elegant regular expressions for some of the functions too (e.g. checkEmail).

Here's the JS Form Tutorial at O'Reilly