How to fit a 2003 discovery headlights into a 1999 discovery land rover?

It's a very involved and expensive process, but instructions are here:

http://www.landyzone.co.uk/lz/f38/discovery-headlight-conversion-2003-lights-71266.html

Lights are on EBay

or try

http://www.roverlandparts.com/discovery-headlights.aspx

or

http://www.partsgeek.com/catalog/2004/land_rover/discovery/body_electrical/headlight_assembly.html