GCFScape has a search/find built in, use that to find the .AIW's from within ther .gcf's. Export those to a folder, then use wtcced.exe to decrypt them if required. You will then need to create a exact match to the gcf's folder structure within your GameData/Locations/ and the game may read your new .AIW's but it might ignore them. If it ignores them than you need to extract the whole track folder from the .gcf, wtcced it, rename the track folder, edited the entries in the .trk to look in the newly named folder, and also rename all the files in the tracs folder to a new name, then edit the .gdb file and change all the entries there too to match your new tracks name. This is all to allow the game to see the difference in the track with each .AIW (stock with in the gcf and your modded one)