FS2002 runway textures are "runwayxx", where xx = a number from 01 to 27, then 64-68, for ex., runway01.bmp, and so on.  I don't know what disc these are on, and I am simply assuming these are correct, I just took a look at them thru my photo browser, they look right.   You could overwrite the whole set rather than try to figure out which are dirt runways.  You probably should first backup anything you overwrite by copying the originals into a temp folder.  If this doesn't work, you may have to re-install.  If so, your add-ons will remain intact.