PHP Form Validation - NEED HELP!!! please ;-)

<title>Border Prints Order Form</title>
<!---Border Prints - Order Form Validate--->
<script>
<!-- 
function MM_findObj(n, d) { //v3.0
var p,i,x; if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document); return x;
}
function MM_validateForm() { //v3.0
var i,p,q,nm,test,num,min,max,errors='',args=MM_valida  teForm.arguments;
for (i=0; i<(args.length-2); i+=3) { test=args[i+2]; val=MM_findObj(args[i]);
if (val) { nm=val.name; if ((val=val.value)!="") {
if (test.indexOf('isEmail')!=-1) { p=val.indexOf('@');
if (p<1 || p==(val.length-1)) errors+='- '+nm+' must contain an e-mail address.\n';
} else if (test!='R') { num = parseFloat(val);
if (val!=''+num) errors+='- '+nm+' must contain a number.\n';
if (test.indexOf('inRange') != -1) { p=test.indexOf(':');
min=test.substring(8,p); max=test.substring(p+1);
if (num<min || max<num) errors+='- '+nm+' must contain a number between '+min+' and '+max+'.\n';
} } } else if (test.charAt(0) == 'R') errors += '· '+nm+' is required.\n'; }
} if (errors) alert('The following error(s) have occurred:\n\n'+errors);
document.MM_returnValue = (errors == '');
}
//-->
</script>
<center><form onSubmit='return validForm(this)' action=send.php method=post>
<font face=arial><font size=2><font color=darkblue>
Your Name:<br><input type=text name=name><br>
Your Email Address:<br><input type=text name=email><br>
Your Home Address:<br><input type=text name=address><br>
Your Postcode:<br><input type=text name=postcode><br>
Town / City:<br><input type=text name=towncity><br>
Choose mount colour:<br>
<input type=radio name="mountcolour" value= "green">green <input type=radio name="mountcolour" value= "cream">cream <input type=radio name="mountcolour" value= "fawn">fawn<br>
Choose mount size:<br>
<input type=radio name="mountsize" value= "10x8">10x8 <font size=1>(7.5 x 5.5 aperture)<font size=2> <input type=radio name="mountsize" value= "10x8">10x8 <font size=1>(7 x 5 aperture)<font size=2><br><br>
ENTER ORDER CODE:<br><font color= darkblue>
<input type=text name=subject value=''><font color=red><br><br><font color=darkblue>
<input type=submit value='Send order' onClick="MM_validateForm('name','','R','email','','RisEmail  ','address','','R','towncity','','R','postcode',''  ,'R','mountcolour','','R','mountsize','','R','subject','','R','');return document.MM_returnValue" style="font: normal 11px arial;"> <input type=reset value='Reset order' style="font: normal 11px arial";>
</center>

  
<SCRIPT LANGUAGE="JAVASCRIPT">
function validate_form(fRef)
 {
 var notChecked = true;
 if (fRef.first_name.value == "") 
	{
	alert("Please enter your first name");
	fRef.first_name.focus();
	return false;
	}
 if (fRef.last_name.value == "") 
	{
	alert("Please enter your lastname");
	fRef.last_name.focus();
	return false;
	}
 for (i = 0; i < fRef.sex.length; i++)
	{
 if (fRef.sex[i].checked == true)
	{
	notChecked = false;
	}   
	}
 if (notChecked == true)
	{
 alert("Please indicate your sex");
 fRef.sex[0].focus();
 return false;
	}
 alert("yep, it worked");
 return false; // remove this line for production mode
 }
</SCRIPT>
<FORM NAME="myForm" onSubmit="return validate_form(this);">
First Name:<INPUT TYPE="TEXT" NAME="first_name"><BR>
Last Name:<INPUT TYPE="TEXT" NAME="last_name"><BR>
Sex: <INPUT TYPE="RADIO" NAME="sex" VALUE="Male">Male&nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="sex" VALUE="Female">Female
<INPUT TYPE="SUBMIT">
</FORM>