Definitely call an emergency vet. I don't know where you are, but here are two numbers near my area (Boston, MA) - we have used the people in Needham, 9 years ago when Miss Hoppy broke her leg at 11:30 on a Monday night. They might be able to tell you whether to soak the foot or ice it down.

Veterinary Emergency Center: Needham, MA: 617-453-0143
Angell Memorial Veterinary Hospital: Boston, MA: (617) 522-7282