prototypejs - getting radio , check box in prototype? -

how can checkbox, radio button, pulldown menu values using id using form in prototype js?

see $f

edit
$f get's text value of element it's id. example if had drop down select box called "month" use $f('month') it's value "february".

in response follow question, "how can count of number of check box selected" use this:

$$('input:checked').length