This may be a bit more rudamentary approach to cleaning 'dirty' headlights, but I know it works. Find a girl you know and ask for nail polish remover with acetone in it. Its the active ingredient, and it will do the same thing for your headlights that it does for fingernails. Just don't use pure acetone, or remover with none at all. Water it down if you have doubts about it. After applying it, rub some compound on it, they should look shiny as new. Its the cheapest way to do it.