I currently have a PayPal IPN script that is working fine.
I will be sending this PP IPN script to you and you will need to create a new WorldPay script that will do the same things as the paypal script.
Basically it will include the following:
1. Create the form
2. Send the payment
3. Receive response from WorldPay after the payment is made.
4. Verify the response, if it's good, run few sql queries (Found in the paypal script).
That's all, simple :)