How should I ....--its a date/timestamp issue

What are your suggestions folks on how to go about setting a date on a form so that a user can not set a start date prior to the current days date? I've been looking around php.net but is it a javascript thing in the validation I should be dealing with, basically as it is I have a form and a user can select a start date, but they should not be able to select a date that is past, currently the start date form is a drop down (a very long drop down) I would like to use one of those nifty calendar popups but am not sure (aka..wasn't able to figure out) how to send the date to the db fields as they are... guidance on this would be great ..how would you do it? thanks guys and gals Terion