To see if there is time, check the days to maturity and compare them to your last frost date.

For most varieties there is probably time in your zone -- I just planted my winter squash here in zone 7.

The true, Dills Atlantic Giant, as raised by giant pumpkin hobbiests, takes an intimidating 10-12feet square though they can be planted in smaller spaces and get smaller pumpkins.

More normal pumpkins can be planted in the center of a 3x3 foot square though you can expect the vines to run out further than that.

I don't know about other places, but around here it seems fashionable for the professional landscapers to plant a long-vined pumpkin or winter squash in the flower beds to use the large leaves as a dramatic accent and a background for the colorful flowers.

If there isn't time for the giant variety this year there is probably still plenty of time for a smaller choice and the giant seeds should still be good next year. :-)

Pumpkins are very easy to grow, but they're heavy feeders so you'll want to work plenty of compost into the planting hill and to feed it a couple times during the growing season.

Dill's Atlantic giants take up much more space than that. Competitive growers prune their plants to a minimum of 400 square feet (20' square) and if left unpruned can take over 2000 square feet. If you want to grow the really big pumpkins I suggest looking at the forum on bigpumpkins.com there are a lot of competitive and even world record breaking growers over there. But to answer the original question it might be a little on the late side to plant the truly massive pumpkins. I also agree that a smaller variety would be better, jack-be-littles are perfect for youngsters and are very prolific with many fruit per plant. Also smaller varieties are easier to grow with minimal experience. If you don't know what you are doing you might not get any pumpkins if you have only one plant of a large variety, however the small ones are basically guaranteed to produce fruit even if you have horrible growing conditions. If you provide a trellis you keep the plants confined to a much smaller space.