A pumpkin is a squash. Just a specific name for a type. Melons ( cantaloupes, honey dews , Crenshaws ) will have similar growing requirements. Water melons are a bit picky about soil types, prefering a deep sandy soil. Pumpkins and melons will tolerate clay and muck soils much better than watermelons.
From personal experience, I grow a fairly big pumpkin here. Water melon did ok, depend on variety I guess. Even fully ripe, my melon won't come close to what available at the market. I guess, the farmers kept their serets of the trade? lol
It's fun, though to grow them and watch them develope at such a fast pace.
Farmer Dill - thank you for the info. The area I'm looking at is very sandy soil at least a couple of feet deep. I planted a walnut tree up there, and just because I needed some place to plant my daughter's pumpkins, I put them around the walnut tree. They took off like a shot! Yep, Mr. Walnut Tree is going to have some more new friends next year.
Lily: I've never tried watermelon before. But with them at $6.00 each in the market, I'm sure going to give it a try next year. I'll just keep working on it until I find a variety that I like.