Can you put left 4 dead on 2 computers?

Yes, there are some emulators (An emulator is something that lets you play games created by different systems on your computer, well, usually on the computer)

In short, yes.

Is it easy? No, it's a huge game.

Are things like N64 games easy?

I downloaded my N64 emulator easily.

Unless you're willing to pay, then, sorry, you may have some trouble.