Well the zip file (if I remember correctly) has not only the track but an "objects" folder, an "environments" folder, and a "cartextures" folder. Open one of those folders, and copy whatever is in it.
Then go to C:/Program Files/NoLimits Coasters v1.7 and then paste what you copied into the folder with the corresponding name. Do that until you have finished with all of the folders in the download.