Hallowskeen, the pattern I originally used for the spiderweb is at

SPIDERWEB TABLE TOPPER

Very basic & simple - just rounds of triple-crochet w/ chains in between... once you do one, you can easily expand on or modify the stitch pattern to suit yourself. I made a big one out of #10 thread that will be on one side of our porch - it's about 4 1/2 ' in diameter. The black one above was made from worsted-weight 100% cotton yarn ("Peaches & Creme", the same stuff you use to make dishclothes & such)

A few more halloween crochet patterns are at: Crochet Pattern Central - Free Halloween Crochet Pattern Links