They are normally allowed to sprawl over the ground. However, I once saw a small variety grown on a sturdy arbor and it was quite entertaining to see the small pumpkins hanging like christmas ornaments. Of course the vine wouldn't support the weight of large pumpkins.
let them run accross the ground..you can carefully turn the stem if it out grows your plot..make sure you give them plenty of food and water ..as they are hungry plants..you can also put some earth on the stems to anchor them ..just in places up the stem..if you are growing one of the giant variety you wont be able to train them up a stem.....have you got any flowers yet?
go to this web site http://www.pumpkinnook.com and you will find everything you need to know..i think those jack pumpkins are the smaller ones...their will be two flowers male and female...the female has a small swelling behind the flower ..hope fully insects will fertilise them for you..i have grown them for years but i grow the large ones..i tried some small ones last year and didnt get much but the weather wasnt kind to me..so its all down to the weather and you can allways try again next year..i have been trying to grow a real giant but have not got their yet..i found this pumpkinnook site and drooled over large ones their..