[Tannaton]

With regard to the headlights - usually they come clean okay with a machine polisher and a semi coarse compound like Farecla G7. I've just done mine for the first time in 5 years and they're like new. Make sure you remove the headlamps and secure them in a workmate or similar to avoid burning through the paint on the panel edges.

With regard to swapping them - whilst the HID (they won't be Bi-Xenon) from a 03 model will physically fit and connect - you are likely to have problems at best with a error message on the dash at worst they just wont work or will flicker.

The headlamp type is programmed into the CEM at manufacture (cannot be changed) and controls how the lights are switched - it's not a simple relay for the dipped beam.