For some reason, I presume legal as always, the first game doesn't come with any of the game music as bonus content (even though it's only a few tracks).

The second games does apparently come with the OST, however.

In any case, you can check out some of the music on YouTube. It's decent imo.

http://www.youtube.com/results?search_query=zombie%20shooter%20soundtrack&sm=12

Especially the menu song - http://www.youtube.com/watch?v=oWLNgDshXeA