Grand Theft Auto: San Andreas Walkthrough

With a visit to the airstrip, CJ meets with The Truth, who insists on a super important initiative called the "Black Project" being hidden in a nearby government facility. When Truth drops CJ off, he has to fend for himself to retrieve the Black Project.

Head inside the facility, being sure to avoid detection by staying out of the light.
Use your sniper rifle to take out from a distance any enemy guards patrolling the area.
From your first spot, several guards will lay straight ahead of you. Take them out.
Guards will be noted by the red blips on your radar.
Inside the compound, head to your right, avoiding detection by the search lights if possible. Inside the control tower, marked by a yellow blip on your radar, you'll be able to enable access to the main stairway down.
If you are detected, you will need to enter through a ventilation shaft. Head to the north-eastern corner of the compound, where it will be marked by a yellow blip on your radar. Shoot out the grating to obtain access.
Now inside, head to the corner of the first room, where you'll enter a long hallway that leads to another open room.
Use your silenced pistol to take out the guard patrolling to your left.
Be careful, as several more guards will be patrolling on the floor below you. Take them out.
Make a left at the red hallway and down to the bottom floor. Take out the guard with this back to you. Several other guards will be patrolling through the bottom sector. Kill them and make your way up the stairs to the walkway. If you follow it to the exit at the far end, you will enter into a room with body armor.
Halfway along the walkway is another opening. Head inside to disable the SAM turrets to help ease your escape.
Make your way back to the bottom sector to head down the long hallway with the metal grating flooring.
Snake around the winding hallways, taking out the guards waiting for you. Use your sniper rifle if necessary to take them out from a distance.
At the end of the twisting hallways, you'll enter into another open area. Scare the scientist into dropping the access key card. Use the body armor if necessary.
For the next area, a long spiraling staircase awaits down a long tunnel. Numerous guards will be waiting, ready to fire up at you. Take out the guard immediately in front of you from entering the room and then use either your M4 or sniper rifle to take out the remaining guards from high up.
If you're unable to see them, slowly make your way around the side, being careful to avoid their guns.
At the bottom of the tunnel is the Black Project -- a jetpack.
Ascend quickly and exit through the top. Head toward the drop-off point deep in canyons, marked by a yellow blip on your radar.
Arrive safely and you've completed the mission.