What you want is to have a check box on the form, and then, you have 2 things to do.
On login, check if the checkbox is checked. If it is, save the user/pass to a cookie. (which means, on load you'll first need to check that cookie to see if you have the data already so you can login straight away).
On unchecking the checkbox, you might want to clear that cookie.
There are plenty of security issues with saving passwords onto the client side, but I'm sure you're either aware of it, or if not, could find plenty of material on it on the net.
Also, you'll have to consider when / why you deleted that cookie ... on logout? only when the user deselects the "remember me", and so on.