Add z_spawn Witch into the console and spam 100 times.
It depends on what map you play, most maps have somewhat the same number of them, except for Hard Rain-sugar mill, which has a higher number of witches because they are attracted to sugar.
No I wish you could tho
4 players can play in Left 4 Dead 2.
Left 4 Dead can be played on either PC or Xbox 360.
Yes, you can play left 4 dead 2 on steam if you buy from Gamestop.
Yes you can play online
You have to download Steam on your computer, then Left 4 Dead 2 can be bought from that.
One can definitely play Left 4 Dead on their own. But it is more enjoyable when other people are dying along with you. :)
which laptop?
nope
Install it.
No, Left 4 Dead does not have a split screen option. The only way to play with someone is online.