2 parts to this script - please make sure the copyright note is left intact to the script maker
=============================================================================
part 1 - please in head
=============================================================================
<SCRIPT LANGUAGE="JavaScript">
/*Cut-N-Paste JavaScript from ISN Toolbox Copyright 1996, Infohiway, Inc.  Restricted use is hereby granted (commercial and personal OK) so long as this code is not *directly* sold and the copyright notice is buried somewhere deep in your HTML document.  A link to our site
http://www.infohiway.com is always appreciated of course, but is absolutely and positively not necessary. ;-)  */


<!--Hide JavaScript from Java-Impaired Browsers

function test_it(entry) {

 if (entry.value!=null && entry.value.length!=0) {

  entry.value=""+ eval(entry.value);

  }

 computeForm(entry.form);

 }

function computeForm(form) {

 if ((form.months.value==null || form.months.value.length==0) ||

    (form.rate.value==null || form.rate.value.length==0) ||

    (form.financed.value == null || form.financed.value.length==0)) {

   return;

   }

 if (!alrt_msg(form.months,1,480,"Your Number of Payments") ||

    !alrt_msg(form.rate,.001,99,"Your Interest Rate") ||

    !alrt_msg(form.financed,100,10000000,"Your Principal Amount")) {

   form.payment.value="A value out of range - Click Reset";

   return;

    }

 var i=form.rate.value;

 ffv=0;

 ffv+=form.financed.value;

 fmv=0;

 fmv+=form.months.value;

 if (i > 1.0) {

 // Hack to mostly correct floating point/binary conversion error

  i=(i/100.0)+.00001;

  var fmt="";

  fmt+=i;

  fmt=fmt.substring(0,6)

  form.rate.value=fmt;

  }

 i/=12;

 var isn=1;

 for (var j=0;j<form.months.value;j++)

  isn=isn*(1+i);

  form.payment.value=(form.financed.value*isn*i)/(isn-1);

  fpv=0;

  fpv+=form.payment.value;

  var fmt="";

  var add=9;

  fmt+=form.payment.value;

  for (var i=0;i<fmt.length;i++) {

   if (fmt.charAt(i)==".") {

    add=i+3;

    i=fmt.length;

    }

   }

  fmt=fmt.substring(0,add);

  fcalc=((fmv*fpv)-ffv);

  var fmtb="";

  var add=9;

  fmtb+=fcalc;

  for (var i=0;i<fmtb.length;i++) {

   if (fmtb.charAt(i)==".") {

    add=i+3;

    i=fmtb.length;

    }

   }

  fmtb=fmtb.substring(0,add);

  form.payment.value="   $"+fmt+"              $"+fmtb;

 }

function reset_it(form) {

 form.months.value="";

 form.rate.value="";

 form.financed.value="";

 form.payment.value="";

 }

function alrt_msg(entry,low,high,prompt) {

 prompt="You couldn't know. "+prompt 

 +" entry has unacceptable stuff: "+entry.value;

 var scratch=entry.value;

 for (var i=0;i<scratch.length;i++) {

  var letter=scratch.substring(i,i+1);

  if ((letter<"0" || "9"<letter) && letter!='.') {

   alert(prompt);

   return false;

   }

    }

 var errtst=parseFloat(scratch)

 if (errtst<low || high<errtst) {

  alert("I'm sorry. "+prompt+ " is not in the range"

  +" from "+low+" to "+high+"!");

  return false;

  }

 entry.value=scratch;

 return true;

 }

//-->
</SCRIPT>
================================================================================
part 2 - enter this where you want it to show up
================================================================================
<FORM METHOD=POST>
<TABLE WIDTH=484 BORDER=2>
<TR>
<TD COLSPAN=3 VALIGN=TOP ALIGN=CENTER>
  <B>Simply Complete These Three Columns:</B></TD>
<TD VALIGN=TOP ALIGN=CENTER><B>See Your Payment Here</B></TD>
<TD VALIGN=TOP ALIGN=CENTER><B>See Your Interest Cost  Here</B></TD></TR>
<TR>
<TD ALIGN=CENTER>Number of<BR>Monthly<BR>Payments</TD>
<TD ALIGN=CENTER>Simple<BR>Interest<BR>Rate</TD>
<TD ALIGN=CENTER>Principal<BR>Amount<BR>of Loan</TD>
<TD ALIGN=CENTER>Your<BR>Monthly<BR>Payment<BR>Will Be</TD>
<TD ALIGN=CENTER>Your<BR>Total<BR>Interest Cost<BR>Will Be</TD>
</TR>
<TR>
<TD ALIGN=CENTER>
  <INPUT TYPE=TEXT NAME="months" SIZE=5 onChange=test_it(this)> </TD>
<TD ALIGN=CENTER>
  <INPUT TYPE=TEXT NAME="rate" SIZE=6 onChange=test_it(this)></TD>
<TD ALIGN=CENTER>
  $<INPUT TYPE=TEXT NAME="financed" SIZE=9 onChange=test_it(this)></TD>
<TD COLSPAN=2 ALIGN=CENTER>
  <INPUT TYPE=TEXT NAME="payment" SIZE=40 onChange=test_it(this)></TD></TR>
<TR>
<TD COLSPAN=2 ALIGN=CENTER>
  <INPUT TYPE="reset" VALUE="Click Here to Reset" onClick=reset_it(this.form)></TD>
<TD COLSPAN=3 ALIGN=CENTER>

  <INPUT TYPE="button" VALUE="Click Here to Compute Payment and Cost" onClick=computeForm(this.form)>
</TD>
</TR>
</TABLE></form>