Phil Plait at Bad Astronomy has written a pretty comprehensive analysis of why astrology doesn't work.
Astrology is one of those areas of nonsense that's never held even superficial appeal to me. I don't just mean the star sign newspaper variety, which is so demonstrably stupid: I mean the entire concept of arbitrary patterns of stars as seen from one particular point in space and ignoring distance from that point and from each other can have effects on our lives that can be calculated with made-up mathematics. Why would anyone even want that to be true, let alone actually believe it?
Anyway, Phil's article is pretty good and has some nice pictures