javascript two action needed on submit

Hi
I have a form that needs post code checking.
On successful completion of the postcode check I wish to open another window (not a new one).
it sounds simple but not being javascript competent, its driving me crazy.
I have copied the postcode check from some one else:

function postit(){ //check postcode format is valid
 test = document.details.pcode.value; size = test.length
 test = test.toUpperCase(); //Change to uppercase
 while (test.slice(0,1) == " ") //Strip leading spaces
  {test = test.substr(1,size-1);size = test.length
  }
 while(test.slice(size-1,size)== " ") //Strip trailing spaces
  {test = test.substr(0,size-1);size = test.length
  }
 document.details.pcode.value = test; //write back to form field
 if (size < 6 || size > 8){ //Code length rule
  alert(test + " is not a valid postcode - wrong length");
  document.details.pcode.focus();
  return false;
  }
 if (!(isNaN(test.charAt(0)))){ //leftmost character must be alpha character rule
   alert(test + " is not a valid postcode - cannot start with a number");
   document.details.pcode.focus();
   return false;
  }
 if (isNaN(test.charAt(size-3))){ //first character of inward code must be numeric rule
   alert(test + " is not a valid postcode - alpha character in wrong position");
   document.details.pcode.focus();
   return false;
  }
 if (!(isNaN(test.charAt(size-2)))){ //second character of inward code must be alpha rule
   alert(test + " is not a valid postcode - number in wrong position");
   document.details.pcode.focus();
   return false;
  }
 if (!(isNaN(test.charAt(size-1)))){ //third character of inward code must be alpha rule
   alert(test + " is not a valid postcode - number in wrong position");
   document.details.pcode.focus();
   return false;
  }
 if (!(test.charAt(size-4) == " ")){//space in position length-3 rule
   alert(test + " is not a valid postcode - no space or space in wrong position");
   document.details.pcode.focus();
   return false;
   }
 count1 = test.indexOf(" ");count2 = test.lastIndexOf(" ");
 if (count1 != count2){//only one space rule
   alert(test + " is not a valid postcode - only one space allowed");
   document.details.pcode.focus();
   return false;
   
  }
  return true;

}
//  End -->
</script>

Code (markup):

my calling line is:

 <input class="submit1" type="SUBMIT"  value="Submit Info. " onclick="postit()" name="Button"  > 

Code (markup):

and my form action call is :

<FORM name="details" ENCTYPE="multipart/form-data" ACTION="../this/that.php"
             METHOD="POST"> 

Code (markup):

All I need is teh post code to be checked for validity and then take me to that.php page, wihtout opeing a new page.

many thanks for your help.

 

Hi
Solved it.
used this instead:

<FORM name="details" ENCTYPE="multipart/form-data" ACTION="that/this.php" onsubmit="return postit()"
             METHOD="POST"> 

Code (markup):

thx