While peace lily is considered a houseplant, it can be put outdoors for the summer in a shady location - just be sure to bring it in when night temperatures start going below 50.
For more information on peace lilies, please visit the following page:
I've never heard of planting one outdoors although they must live this way out in the wild. It's just that they're so nice indoors I'm not sure I would plant one outside. I'd be interested in knowing how it does. Just treat it the way you do indoors in the pot - only water it when the soil feels dry, and don't let it get too much sunlight.