date validations

I have two parts of a question. First I have several dates in my app which aren't required, so I don't think I can use a date_select right? There doesn't seem to be a way to give the user an option to *not* select a date.

So, assuming I need to just give the users a form field, anyone have a good piece of code for checking the validity of a date, allowing various forms, i.e.: 12.12.2007 12/12/2007 12-12-2007

Any suggestions?

Thanks, Joe.