I think that Watermelon is a cinch to grow, but I'm in a climate where we can harvest, most years, into late October before it gets too cool to sustain
plants such as
peppers, Tomatoes & Melons. I'm not sure that the Minneapoils/St Paul area is far enough south to give you a good enough advantage to take them all the way to harvest, but I know people who have done it with success in your
zone.
You'll need to begin with an established
plant that has been started indoors & taken all the way past the maturity of true leaves, &
plant when the ground is already warm, to get a jump-start on the time they'll need. (Go with a variety that takes under 75 days to harvest.)
Melons DON'T like a lot of water, which is something that surprised me when I first got started raising them! Because their fruits have such a high water content, I thought they needed all the water they could get!
WRONG! I almost hate to pick them, cuz they're so picture-pretty!
Best of luck, & happy 2006 gardening!!