Street water valve won't shut off
If you're talking about one of the meter stops that has a hole in it for locking purposes, the city will need to replace those. Usually, the city stops are ball valves and don't have problems like that. Sounds like you have a gate valve a little ways away from the meter.
If that's the case, you'll need to shut off the meter using the stop on your side of the meter. If it is really hard to turn, stop and ask the city to come shut it off. If you break it they will charge you a lot to come fix it.
Once you have it off you'll need a new valve and possibly a union depending on how far away from the meter union the valve is. If you're really close to the meter union you may be able to use that for your union instead of buying a new one.
What kind of piping is in the ground? If it's galvanized, I wouldn't recommend doing anything with it, and just use the meter stop to turn your house off.
I wouldn't call this a hard project ,but there are a lot of variables that could turn it into a pretty difficult project very quickly.