Shouldn't be much more difficult than F150 ones, which use the basic instructions of leaving in 200* oven for 10 minutes, start seperating, restick in oven every so often to resoften sealant.
On the other hand, you could probably get some cheap OEM black headlights on ebay. I usually see them for 20-30 bucks (not including shipping) each.
Here's a couple:
http://cgi.ebay.com/ebaymotors/03-0...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
http://cgi.ebay.com/ebaymotors/Ford...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
etc. Just remember that on ebay, "03 Expedition headlight" and "2003 Expedition headlight" are two different search quarries. Go from 03-06 and 2003-2006, each year individually.