How should I store my tires?

I have a pair of ET streets on salad shooters that I need to store for the winter. Should they stay on the rims? Full of air or not? Should I stack them or set them on their tread? If there is an easy way to preserve their condition I would love to hear it. I just don't want to look at them in the spring and see that I have a $300+ pile of junk.

thanks
Dustin