I can't remember the security code for my Nokia 2760 as I only use it very rarely when calling abroad. It is Orange PAYG - can anyone help with unlocking it please ?

You tried ringing up orange from another phone and ask them to unlock it for you? they should give you the PUK code

The PUK wont help with a forgotten security code, only with a wrong SIM pin.
All you can do is take it to a Nokia service centre who may be able to reset it for you, but will probably charge. There are some sites on the internet who will reset the security code if you send the phone to them, expect to pay £15 or so. Similarly with a local phone shop.