I have a web page without form in it, but it has input fields(email address, password).

Why do you want to fill out fields you can't submit? The FORM element specifies the url to which the fields are to be submitted. This isn't just theoretical. I tested a submit button outside of a FORM, and clicking it did nothing in FireFox. It could be that the fields are being used by JavaScript, but WWW::Mechanize doesn't process JavaScript.

PS - Just in case you care to know, it's actually illegal to have INPUT elements outside of a FORM element in HTML.