Steam

One of the easiest ways to get started with zombie games is by downloading STEAM. It is free to download, however you pay for retail games through it.

The reason I suggest getting it is because

1. It makes it easy to search for games, and find communities for that game.
2. It has sales on a regular basis on its games for up to 90% off.

I personally buy all my games through it. My next post will be on a game I purchased through steam for only 5$. If you have steam, leave your gamer ID in the comments and I will add you.