Easy and safe method
The best and easiest way I have found to remove old paint jobs is to pick up some Simple Green from your local Home Depot/Lowes or Wal-Mart. The stuff is environmentally friendly, so you can pour it down the sink when you are done. It smells pine-like, but the smell fades in a few days.
All you have to do is soak your miniatures in a mixture of 3 parts Simple Green, 1 part water for roughly 48 hours. The paint will come off easily after that. Just use an old toothbrush or scrub brush and some running warm water.
Good luck!
Aegis