Ok, lots of older cars have a problem with hanging doors. You have two options on how to fix this. You can replace the doors or the hinges or both. If it's hanging only replace the hinges, 1 upper and 1 lower per door. Now, if your door is rusted you may want to replace the entire door.
Third, have someone hold the door open (use a jack, too) while you remove the hinges and remove the door. Then with the new hinges you got already (you knew that, right?) take 'em and bolt 'em on to the new door. If the new door has hinges that look in order, you can use these. New hinges are recommended though. You may as well replace 'em while the door's off.
Fourth, have someone hold the door again while you line it up. It's also useful to use a jack of some sort, or some type of immobile support to hold the door in place, but have a person hold it for steadiness. Connect the top bolts, do not tighten completely. Connect the bottom bolts, again do not tighten completely. Make them snug. Remove the supports and shut the door gently (remember the bolts aren't 100% tight).
Fifth, while the door is shut, check to see if the "crease" where the front of the door meets the bode is even. Also, check the bottom of the door for alignment to the body. If it needs to go up or forward a little, you've gotta open up the door and while one person looks at the hinges, the "adjuster" moves it forward or up or whatever's necessary. When you think you've got it, tighten the bolts to the frame.
Sixth, if you lucked out and got it lined up right the first time, you're done. Otherwise, continue step five until you've got it to where you're happy with it. The doors should now shut like new. Grease 'em up and you're good to go (to the body shop to get the doors painted to match the rest of the car).
Second, throw the old hinge accross the room 'cuz you're pissed off you have to do this. Then take the new hinge and bolt it in where the old one was. Make sure that you are bolting in another upper hinge (as opposed to lower).
Third, do the same for the bottom hinge as you did with the top hinge and go to step four.
Fourth, see step five in the above section ("New Doors") and follow that 'til completion.
I hope this is helpful. Rex.