Acetone
Acetone is about the only thing that will remove nail polish - that said, acetone will also remove just about every floor finish you can imagine - it will attack a poly finish, a resin finish, a lacquer finish and anything else you can think of.
One trick you can try - if your finish where the nail polish is was very new - IE shiny and not scuffed, try ice or dry ice to completely harden the nail polish, then with a VERY thin sharp knife, try to get under the polish edge (if they didn't try to wipe it up) and pop the polish off the floor, you may get some minor marks from the knife and some dull spots where the polish attacked the finish while it was curing, but you can hide that with Future floor polish.
If resorting to acetone - About the only thing you can do is to dab it on the nail polish ONLY and try and work it off without getting any on the surrounding finish.
If it dulls the surrounding finish, try bringing that back to a shine with a coat of Future floor polish (might as well do the whole floor when you've got it cleaned up), or do the spot with a car buffer very carefully so as not to burn through.