how can I combine two input fields to send to the same database field?, html forms Options

[supasnail]

I am wondering if this is now possible now that i've been googling for ages, but someone might know the easy answer ...

What I would like to do is allow two or more input fields in a form to be combined and sent into the same database field....,

for example, rather than allow users to insert the date in any format they choose, I'd like to steer them to inserting it YYYY-MM-DD, ideally i'd like this to be in the form of three separate input boxes but I don't want three fields in the database, just the one.

Is there a way to do this with simple xHTML? or will this be a javascript combo? I'm sure it can be done.

Hope I have been clear enough..

Thanks