If you're talking about the serial number, it is on the jewel(spine) of the CD case it came in. If you're looking for a cracked version you're asking in the wrong place because WikiAnswers does NOT tolerate with piracy.
On the back of the game manual/CD case, or on your Steam account.
4 players can play in Left 4 Dead 2.
It is a Key that will unlock the Left 4 Dead 2 in your steam library
Yes there is split screen for left 4 dead 2.
You can purchase The Sacrifice DLC for Left 4 Dead 2, which has you play as characters from the first game. Additionally, you can put character skins of the original characters onto the characters of Left 4 Dead 2 (Only in the PC version)
On the back of the game manual/CD case, or on your Steam account.
no, left 4 dead 3 would not have the same characters as in 1 or 2
left 4 dead 2 can be downloaded from Steam
No, Left 4 Dead 3 is not coming out. There is only Left 4 Dead and Left 4 Dead 2. Both fun games.
4 players can play in Left 4 Dead 2.
You can't get The Passing on Left 4 Dead 1. It is only a DLC for Left 4 Dead 2.
Not Left 4 Dead 1 or 2, but Valve and Havok announced the Haggard in Left 4 Dead 3.
Yes it does.
Left 4 Dead 2!!
It is a Key that will unlock the Left 4 Dead 2 in your steam library
If you love zombie games then you'll love Left 4 dead, they also came out with Left 4 Dead 2.
Steam's Left 4 Dead and Left 4 Dead 2 engines have eliminated bunny hopping.