Playing round with refresh rates and scanlines from googling the net results in the TV displaying the picture but at strange states such as 1125i and 765p (this is what the TV displays on screen) - I can never seem to get standard 1080i or 720p - anyone know why?

1125i is probably a good alias to 1080i.

It is similar to PAL 576i, which is actually 625i, but those about 50 scanlines are for sync signals and porches.

765p is odd, it should be 750p. HDTV 720p is 720 scanlines and 30 lines on porches and sync.

So I am not sure about if your TV reports this as total number of lines, or are modelines wrong in your configuration.

Best regards, Jori