Any way to add 'onchange' to a 'select' helper?

I basically have a select menu with two options:
– Leave password unchanged –
– Enter new password below –

I want my form to use a sexy prototype effect to SlideDown the text
field when the second option is selected. That way the user isn’t
confused by a blank password field when they’ve selected to leave the
password unchanged.

Can I do this with Rails’s ‘select’ helper? Is there something like
‘:onchange => foobar’ that I can use? Or do I need to write out my own
select tag for this?

Thanks! - Sean