No worries!
Most FMS files seem to zipped so you will have to download and unzip them into the 'model' directory/folder of your FMS program. For this you will have to use a program such as winzip. You can download a free copy from here:
http://www.winzip.com/index.htm
Make sure that the unzipped files are sitting in the 'model' folder and not in a sub-folder, otherwise you will have to cut and paste them in.
Open FMS and under 'model' in the top tool bar select 'load' and choose your plane. Easy!
Hope this answers your problem!