i'm assuming that when you say "Mailto script" what you mean, is a form that has it's action set to "mailto:someguy@someplace.com".
if that's the case, then see the following link for a nice little tutorial on how to do this:
http://www.htmlgoodies.com/attachp2.html
if that's not what you're talking about, then you're going to have to provide some actual details.
hope that helps
ps: as with your other post, because i don't think that this is going to have anything to do with javascript, i'm moving it to the HTML & CSS forum