Validating that submit date isn't in the past

I think it's pretty easy, but I'm a javascript newbie so some help is appreciated.

I need to check if a date submitted by a form isn't before todays date. But how?

Any help is welcome.

Jeroen

When you say date submitted by a form do you mean the user inputs the date into a text field? And when you say todays date do you mean your server's date or the date on user's computer? The user's date, which is the one accessible by javascript, can be changed to whatever the user wants...

The input is given by the user (say a date on which he wants to rent a room.)

Javascript takes the localsettings of the user, so those are what we are dealing with then.