MyCustomProduct.php

<?php

class MyCustomProduct extends ProductPage{

	/* ... */

	public function ProductOptionsForm() {
		$form = $this->StartForm();
		$form .= $this->AddBaseProductDetails();
		$form .= $this>ProductOptionsSet();
		$form .= $this->MyCustomField();
		$form .= $this->AddToCartForm();
		$form .= $this->EndForm();
		return $form;
	}

	public function MyCustomField(){
		return "<label for='MyCustomField'>My Custom Field</label><input type='text' name='MyCustomField' value='' class='myCSSclass'>";
	}

}

class MyCustomProduct_Controller extends ProductPage_Controller{

	public function init(){
		parent::init();



	}

}