Need Help Debugging Script/Error in Script - Help with submitting form using form.submit ()

Help! I am new to JS and need to submit a form using JS using a "button" VERSUS using submit. Below is the code that I have entered in my contact page. When I click the submit page I get the following error:

Error: Object doesn't support this property or method. I am new to JS and need to get this page completed and I am driving myself crazy! Please HELP ME!
==================================
[code]
<script language="JavaScript" type="text/javascript">
function checkForm(thisform)
{
if(form.name.value=='')
{
alert("Name field is required.");
return false;
}
if(form.phone.value=='')
{
alert("Phone number is required.");
return false;
}

// Check email address

if(form.email.value == "")
{
alert ("You must include an accurate email address.");
email = document.f1.Email.value
AtPos = email.indexOf("@")
StopPos = email.lastIndexOf(".")
Message = ""
if (email == "")
{
Message = "Not a valid Email address" + "\n"
}
if (AtPos == -1 || StopPos == -1)
{
Message = "Not a valid email address"
}
if (StopPos < AtPos)
{
Message = "Not a valid email address"
}
if (StopPos - AtPos == 1)
{
Message = "Not a valid email address"
}
return Message
}

if(form.email.value == "")
{
alert ("You must include an accurate email address.");
}
if((form.email.value.indexOf ('@',0) == -1 ||
form.email.value.indexOf ('.',0) == -1) &&
form.email.value != "")
{
alert("Please verify that your email address is valid.");
}

// if all is OK submit the form
document.form.submit();
}


.
.
<form action="message.php" method="post" name="form" id="form">
.
.
.
<input name="submit" type="button" id="Submit" onclick="checkForm(this.form)" value="Submit"/>