While I certainly agree that something must be done, I don't think banning/outlawing guns would prevent this kind of thing.
Do you think the guns used in this shooting were legal/registered? No way. I'm sure they were bought on the black market/smuggled in. All the laws in the world won't stop that.
What needs to be done,is like Pete said, implement a "0 tolerance" law regarding weapons. You use a weapon in a crime, it's a felony - minimum sentence of 25 years.
Mind you, like I said - I seriously doubt such a law would stop the gang shootings. I really don't think they care about laws - if they did, do you think they'd open fire on the public? Exactly.
I think a 0 tolerance rule regarding gangs need to be in place. Make gangs illegal. Get a couple hundred officers, and start arresting gang members - just for being in a gang. I'm willing to bet we'd see a lot of additional charges (guns, drugs) being laid after they are arrested. Not only that, but a lot of the gang members are "imports" from other countries that can be/should be deported quickly.