Thinner needles help with this problem, and make sure you always use a brand new needle when you sew with lightweight fabrics. If it's still puckering, you can try sewing with a thin piece of paper against the feed dogs. This will keep the fabric from slipping into the machine, and can be torn off easily when you are finished with the seam.
Good ideas, I'll have to look into what I can get. I'm sure I can get a shower curtain for cheap. I know I need something stronger to tie the ends down with. Would it work to use one of those short bungee cords?