Nail polish is some nasty stuff that you certainly don’t want on your carpet or clothes, and it might seem like something that will be near impossible to get out, but it’s not–it’s nowhere near as bad as blood or red wine, and if you handle it properly you can not only get out a fresh stain very easily, but you can even almost completely remove an old stain, as well.
There seem to be two different methods circulating the net that people uniformly agree works, one better than the other: Windex. Yeah, ammonia-based glass cleaner like Windex beats everything else. Something everyone does agree on.
The other method is to use hydrogen peroxide and baking soda, which might be more along the lines of a pre-wash sort of treatment that sort of softens the stain up before you hit it with the big guns, check it out (btw, loved the Pulp Fiction reference at the end, that was cool 😉 ):is that nail polish remover (especially if it’s acetone-based) does not work well, it tends to smear without removing the stain and if it’s acetone-based it can literally bleach out the carpet if it’s any color other than white.
Additional Resources and Further Reading
LONG list of tips and tricks for removing nail polish from various things at WikiAnswers
More tips from CreativeHomeMaking.com (notice the general consensus that Windex works best)