I have found where to put the URL in Worldpay but it still isn't going back to the site? To enter the callback URL you have to log into your admin area, then go down to the bit that says Installations for whatever, you should then see your site name with (select junior) next to it, on the right hand side click on configuration options which opens up a new screen. Here you can enter the callback URL and then you need to tick the box that says callback enable and I believe the other box that says use callback response. I haven't managed to get this to work yet. It worked once for me when I did a test. I recieved an order through OSCommerce and an email from worldpay to say the payment had been made, but I have had to use recover cart option to get the customers orders ever since then. Not sure why this is? if you manage to get it working properly please let me know
Hope this helps
Lisa