adding php statement ! please help

In module checkout_process
i want to add a if statement that will do :

If the buyer choosed payment methode bank
the mail should give him my bank account and he should enter
the order number as message of the payment

ex:
if
define('EMAIL_TEXT_PAYMENT_METHOD', 'Payment Method');
if the payment method was "bank"
My bank number is .......... and your id transfere should be
'EMAIL_TEXT_ORDER_NUMBER

I hope you can help me to add this statement in the beginning of that php




define('EMAIL_TEXT_SUBJECT', 'Order Confirmation');
define('EMAIL_TEXT_HEADER', 'Order Confirmation');
define('EMAIL_TEXT_FROM',' from '); //added to the EMAIL_TEXT_HEADER, above on text-only emails
define('EMAIL_THANKS_FOR_SHOPPING','Thanks for shopping with us today!');
define('EMAIL_DETAILS_FOLLOW','The following are the details of your order.');
define('EMAIL_TEXT_ORDER_NUMBER', 'Order Number:');
define('EMAIL_TEXT_INVOICE_URL', 'Detailed Invoice:');
define('EMAIL_TEXT_INVOICE_URL_CLICK', 'Click here for a Detailed Invoice');
define('EMAIL_TEXT_DATE_ORDERED', 'Date Ordered:');
define('EMAIL_TEXT_PRODUCTS', 'Products');
define('EMAIL_TEXT_SUBTOTAL', 'Sub-Total:');
define('EMAIL_TEXT_TAX', 'Tax: ');
define('EMAIL_TEXT_SHIPPING', 'Shipping: ');
define('EMAIL_TEXT_TOTAL', 'Total: ');
define('EMAIL_TEXT_DELIVERY_ADDRESS', 'Delivery Address');
define('EMAIL_TEXT_BILLING_ADDRESS', 'Billing Address');
define('EMAIL_TEXT_PAYMENT_METHOD', 'Payment Method');

define('EMAIL_SEPARATOR', '------------------------------------------------------');
define('TEXT_EMAIL_VIA', 'via');

// suggest not using # vs No as some spamm protection block emails with these subjects
define('EMAIL_ORDER_NUMBER_SUBJECT', ' No: ');
define('HEADING_ADDRESS_INFORMATION','Address Information');
define('HEADING_SHIPPING_METHOD','Shipping Method');
?>

to be more clear

When the customer finish the order and press confirm


a mail will be sent to him from the module order_checkout

i want in the begining of the mail to be like this "invoice":

dear .....

You choosed to pay by bank:
our bank number is : ............
your ocr number is : ............. (it will be his order number so when i check the bank i know who payed)

i want it in if statement cause if he choosed another payment methode it means he already paid and he dont need my bank info