Even the most careful painter gets accidental paint on kitchen cupboards. As a general rule, the faster you clean it off, the easier it will be to remove. Even old, dried paint can be removed from almost any cupboard surface, whether it's varnished wood, melamine, metal or finished particle board. As long as the paint is water-based, this should not take much effort. If you're dealing with old, dried solvent-based primer or paint, it's a lot trickier and may not be possible without refinishing the underlying surface.
Things You'll Need
Latex paint remover
Clean the paint as soon as you can. Use a rag dampened with water for water-based paint, or mineral spirits for solvent-based paint. If the paint is still fresh, it will come off easily.
Soak a rag in hot water and hold it over dried water-based paint for a minute or two. The hotter the water, the better -- the combination of heat and water will soften water-based paint. Scrub it gently with a kitchen scrub sponge. If it's a blob or drip, use a plastic scraper, credit card or even your fingernail to scrape away the blob.
Rub the paint with a commercial, solvent-based latex paint remover if the paint is stubborn. Sold in paint and hardware stores, this product will remove old, dried water-based paint but will not harm most cupboard surfaces.
Rub acetone on factory-finished metal or melamine cupboards, turning the rag frequently and adding more acetone as needed. Acetone will remove most types of dried paint but isn't harsh enough to damage most factory finishes. Don't use acetone on varnished wood cupboards because you'll be left with a dull spot. If you don't have acetone handy, use nail-polish remover -- most contain acetone.
Mineral spirits have no effect on dried water-based paint. Test any sort of solvent on a hidden spot on your cabinets first to make sure it won't mar the surface.
Don't use chemical paint removers. Anything that removes old, hardened paint will almost surely remove the underlying finish from the surface of your cabinets as well.