Old house has three prong... new dryer has 4 prong... can I change dryer to a three prong so I don't have to call expensive help? Iunderstand I may have to add a ground wire to the new dryer? Thanks,mark

The electrical code requires the 4-wire connection that your dryer has. Since the house is older than the code, it has a 3-wire outlet.

You can put a 3-wire cord on your dryer, but pay special attention to the grounding strap. Here is a good reference.

This page has some good photos (follow the links).

Since the fourth wire of a 4-wire cord is the ground (which you won't have), you'll need to ground the frame of the dryer with a strap or wire to be safe. Do not skip this step!

Best of luck,
WallyH