Hi Ringo,
Thanks for the info, helped a lot, looks like that service is setup in "Compatibility Mode for SP02" mode. So using 'X-Requested-With=XMLHttpRequest' allowed me to post modifying requests.
(Apologies for the ignorance on the SAP side of things, I'm not a SAP guy, just a developer trying to integrate with a client SAP system).
Cheers,
Tom