Wilting that is not due to a problem with water supply can be caused by disease. Pumpkins can be prone to bacterial wilt which is a bacterium spread by insects. Unfortunately there is no effective treatment for this disease and and any sick plants will have to be removed from the garden to prevent it from spreading. You can try and test your plants for this disease by cutting open a stem close to the crown of the plant. The bacteria may ooze out and will appear white. There is a good picture in this information sheet.

http://www.extension.purdue.edu/extme...

How long have the plants been like this? This disease is quite fast acting and can kill young plants within a couple of weeks.

With regards to the fence, do you mean trellis? It would depend on the kind of pumpkin you are growing, most grow quite low and have heavy fruit which may not be supported if you have the vine growing too high. You can build a lower support by nailing together some wooden beams into a square or rectangle and overlying some poles on which to place the vines. I would take care of the wilted plants first though!

Let me know how you get on,
Lindsay