The stock ones should have clips. I don't know how to remove those. To fit there is a clip in the fenderwall in the corner. On the edge of the sideskirt there should be a hole that lines up perfectly with that clip/hole in the fender. Line up the side skirt and then mark where the holes are because you will need to drill. The 2000s do not have the holes for the sideskirts. I used self tapping sheet metal screws (1/2-1). You will need about 12 for each side. Make sure when lining up that the sideskirt touches the lip on the "frame" or else the sideskirts will stick out.
I know the pain. Yesterday I installed SE sideskirts on my 2000.
But it is worth it.
Also, what will I have to do to get them to fit? Are they a perfect bolt on, or do I to drill holes? I heard someone say you had to drill to get them to fit, but maybe they were talking about SVT side skirts? I know the 99s were identical, so why wouldn't they just bolt on? As alway, thanks! 
