Grand Theft Auto: San Andreas/Intensive Care

This first mission for Paulo is actually for Ken (another Vice City character) who is worried over a mob member who is in the local Hospital. Head over to the hospital and enter the mission marker, you hear a conversation off-screen between CJ and the Hospital Receptionist in which she tells you that Johnny has been collected by an Ambulance, three red blips appear on the map/radar and it's up to you to determine which is the Mafia wagon. Pick a blip (doesn't seem to matter which one) and head off towards it, when you get near you will be told to ram it to gauge the driver's reaction. If the Ambulance stops and the driver gets out it's genuine and you need to head off after the next blip. Otherwise the Ambulance's Siren starts up and the chase is on.

Assuming you've got the Mafia one, you'll be invited to rough it up a bit to "show you mean business". Eventually it'll stop and the mobsters will get out and start shooting, pick them off (you did bring a gun right?) and nick the Ambulance, you'll be told to head for the "Meat Factory" which is up north on the outskirts of town. Get there quickly and you might not even see the pursuing mafia cars, drive into the marker to end the mission after a short cutscene.

Tips
There's going to be lots of paint-trading going on on the streets of Las Venturas as you bash Ambulances so you'll need a sturdy vehicle, there's often a Patriot (Humm-Vee type vehicle) in the corner of the Hospital parking lot so that's a good bet.

Another option is to grab a Seasparrow. Simply land it on top of an ambulance to see if it is real or fake. Once you find the real one, a few rounds of the Seasparrow's minigun will suffice.

Rewards

 * Cash: $5,000
 * Respect +