[JayCat]

When someone gets VAC banned, it only bans them from games that run that certain engine. You might see someone playing cs that has been VAC'd. The game that they were banned from might have nothing to do with cs. But you know what they say about cheaters.  :

in other words, banned in 1 valve game, means banned in all valve games. am i right?

Not quite. It depends on what engine that the game runs on.
For example, CS 1.6 runs on the HL1 engine. So if you get VAC'd from 1.6 you also get banned from all of the games that use that engine.

Counter-Strike 1.6
Counter-Strike: Condition Zero
Day of Defeat
Deathmatch Classic
Half-Life
Opposing Force
Team Fortress Classic
Ricochet

CS:S uses the HL2 (Source) engine. So the same applies. If you're VAC'd from CS:S you are also banned from the following.

Counter-Strike: Source
Day of Defeat: Source
Half-Life Deathmatch Source
Half-Life 2: Deathmatch
Team Fortress 2