I got the game yesterday, and here's the way I did the part in the alley without shooting once so far in the mission (the alley is the part right after the time your boss tells you you can go in the streets)
When you exit the underground passage, you find yourself turning left, then at your right, there are stairs that go downwards, with two policemen "interrogating" a civvie.
At the first left turn, right when exiting the building, stay there. Position yourself, facing the wall where you just came from, and very near the edge of teh said wall, but not too far, since you'll be grabbing the edge on the LEFT side.
// MINI-MAP:
Legend:
| & = -> walls
. -> down stairs
: -> up stairs
X -> position
) & ( -> ledges
ENTRANCE
| Â Â Â Â Â |
| Â Â Â Â Â |
| Â Â Â Â Â |
| Â Â Â Â Â |==============|
| Â Â Â Â Â X Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â |
| Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â |
|==============Â Â Â Â Â Â Â |
     |)           |..........|
     |)           |..........|
     |)           |..........|
     |)           |..........|
     |)           |..........|
     |)           |..........|
// END MAP
So, you face the position AWAY from the stairs, and do a wall jump. If you do it right, you should grab the second ledge, way over every light, nearly at the same position as the balcony at the other side of the alley.
Go all the way to the other side, without dropping. Once you ran out of ledge, you should be in the corner, next to the two guards on the opposite wall, and nearly under the balcony. Let yourself fall and do a silent landing.
SAVE HERE
Stay in the bushes until the guard that walks up and down the alley turns away from you.
If you time it right, you should be able to easily go half-way into the little alcove, on the right, where there isn't much light before the guard comes back. Once he's back the way you came from, wait.
When he passes again the direction you want to go, follow him closely.
Sometimes, I found the timing with the civvie on the balcony doesn't fit. Then, it's usually when the guard just passed your way, going in the direction you came from, that you have to do it. if the civvie sees you, you're toast.
Once passed that, the rest should be obvious.
NOTE:
So far, I'm trying to get in the embassy without killing the last guard, but the darn civvie always sees me, and the only bullet I used was on the light at the entrance of the gazebo-type passage...
I'll see what can be done for that darn part later...