Dear God, another il-informed newby...

[camp]

Hi davidbrook,
Begin.. about tutorial look at: XS++ 3.1 Guide-Flashing,Customizing,Recovering - Top Sony Forums (it's perfect, i use it to flash my w810i).
About Main and FS you can download in firmware subgroup of download section (have to pay a little for it). Also is necessary the Customization file in order to finalize the phone. You have to choose Main, FS and Custom according your original firmware version and, most important, according to your cid (a sort of protection against flash). w810 can be cid49 or cid50. my w810 was cid49, you must watch the initial log in xs++ after to have connected the phone as written in tutorial. If you post your phone log the forum can be help you easily. About flash menu is suggest to upload later (alwais the same tutorial). I hope to be clear