Question
I recently moved in with my in-laws and have taken on the task of whipping the vegetable garden into shape.  One outstanding problem are a couple of grape vines that were planted last season.  She never built any structure to grow them on, nor has she pruned or maintained them at all.

If it were up to me, I would just get rid of them, but she wants to keep them.  Now that they're very established (and a giant tangly mess) is it too late to build a structure, prune and train a few vines?  Everything I've tried to search about grapevines is info on getting them started properly, I can't find info on what to do to fix an improper job.

Any suggestions or a point in the direction of resources would be greatly appreciated!

Answer
Ahh, grapes. I have visions of Lucy and Ethel, stomping grapes in the episode where the Ricardos and the Mertzes visit Rome.  Not your mother-in-law, eh?  No worries; we will get those rampant grape vines in tip-top shape, but it may take a season or two and plenty of patience.  In fact, you might one day even like them!  
I don't suppose you know which type of grapes you have, do you?
Neglect of grape vines usually results in a tangled mess, not to mention poor feruiting because the vine "over-vegetates" (translation: produces too much foliage). Because your vines are not yet mature, you need to decide how you want to maintain them from now on.  Grape vines are considered mature at about three years.
If space permits, I recommend building what's called a "cordon."  This is a simple structure, akin to two sturdy posts connected about 5' off the ground by a very sturdy (but slender) pole or thick wire.  
As for pruning, you want to wait until the vine is dormant, and in Pennsylvania that means winter. If you can stand it, wait until February, and then you can attack this year's growth.
Find the biggest, healthiest vine there is, and prune each "cane" -- branch -- back to about three or four nodes.  The cut end of should be about as thick as a pencil. Don't worry about how much you're removing; more than 75% of the one-year-old wood will need to come off during dormant pruning of one-to-two year old vines.

One of the best resources for maintaining healthy grape vines is actually your next door neighnor, Ohio State University.  I highly recommend their site.  Here is a link to a fact sheet  that even has good pictures of what you want to end up with:   http://ohioline.osu.edu/hyg-fact/1000/1428.html

Your mother-in-law will be thrilled, I promise.  And you will get major points.