Yep, the BIC (for regular Civ3) or BIX (for Play The World) is the file you tinker with when you open the editor.
About the order: When the game looks for an icon for a luxury, it starts the search from the first luxury in the BIC/BIX file, and then starts counting
all resources afterwards. So if the next luxury resource in your BIX file is 6 places after the first, you will need a gap of 5 blank squares horizontally and then add in the next luxury icon in the 6th square.
Take a look at the Luxuryicons_small file from the DyP mod. Kal-el numbered the first row when he was figuring out how this works. (the second row has letters, but that was just to test if the game used the 2nd row at all)
Our first luxury is Wine, so the Grapes icon is the first in the PCX file. Then, in the order they appear in the Double Your Pleasure BIC file we have:
Furs (Lux)
Dyes (Lux)
Incense (Not lux, but we have been too lazy to remove the icon)
Spices (Lux)
Elephants (Not lux, same reason as Incense)
Silks (Lux)
Gems (Lux)
Whales (Not lux - would be using the square numbered 17 if it was a luxury)
Game (Not Lux, would be #18)
Fish (Not Lux, #19)
Cattle (Not Lux, #20)
Wheat (Not Lux, #21)
Gold (Not Lux, #22)
Cotton (Luxury, so there is an icon in that spot)
.. and luxuries all the way to Wool (Sheep Icon) and then we don't have anymore luxuries in the file.
I hope that helps a bit more
