Re: Leaky main shut-off valve
If your meter is accessible, there should be a shutoff valve just upstream of it. You should be able to give this 1/4 turn clockwise to shut off the water. Usually, this valve doesn't have much of a handle; if you use pliers or a wrench you'll probably skin your knuckles and exclaim loudly. The proper tool for the job is called a "meter key".
By leaking, do you mean that it's dripping and getting the surroundings wet, or that you shut it off and it doesn't shut off completely?
How you replace the valve depends on the type of pipe you have. If it's galvanized steel, cut out the valve and about 6" of pipe on each side using a tubing cutter or hacksaw. Get a ball valve the right size and two nipples, sized so that when threaded into the ball valve the whole assembly is around 1/2" shorter than what you cut out. Get two compression couplings sized for that pipe, and use them to install the replacement valve. Make sure that the existing pipe is clean & not rusty. If it's rusty, you may need to sand it with emery cloth so it's smooth.
If it's copper pipe, you can do something similar to the above, but do not mix copper & galvanized steel pipe or fittings. That's a recipe for leaks. It's OK to mix steel pipe and brass/bronze fittings.
The best way to do this with copper pipe is do something similar to the above, but instead of using compression couplings, solder the new pipes & valve in using copper repair couplings. Look ****** for instructions for soldering copper pipes, and practice on a couple of scrap pieces before doing it for real.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.