Limitation - If Fields Not Empty Run Rest Of Code

I am building some JS and would like to share my limitation. This is the code:
Code JavaScript:
<script language = "Javascript">
function onComposeSubmit() {
var formDOMObj = document.Login;
var TrocaImagem
if (formDOMObj.email.value == "" || formDOMObj.anexo.value == "" )
alert("<%response.write Idioma.Item(Session("Idioma")&"_10")%>")
TrocaImagem= "1"
else
TrocaImagem="0"
return true;
return false;
// change button
if TrocaImage="1"
document.getElementById("submitButtonDiv").style.display = "none";
if (navigator.appName == "Microsoft Internet Explorer") {
document.getElementById("progressBar").innerHTML = "";
document.getElementById("progressBar").style.display = "block";
document.getElementById("progressBar").innerHTML = "<img src='img/progressbar.gif' alt='Progress Bar'>";
} else {
document.getElementById("progressBar").style.display = "block";
} else }
</script>

Things I am trying to Do:
- Check if email field isn't empty and check if the anexo field isn't empty. Actually I would like to have it separeted but I dunno how to do this.
- If email and anexo isn't empty run the change button part of the code, witch will change the submit button for a progressbar.gif image. Actually this part of the code works great but without the field validation above.