Whee! XNA port of Zombies. Pretty much, this means that it will run on Windows, and only windows, but that I get access to a much more powerful engine.
Download the archive
here, then run either the setup.exe or the application manifest file. Either one will work.
Then you run the file off the Start menu.
During the installation, it will download and install the XNA runtime redistributable if you don't already have it, so no separate file to hunt down. On the downside, Microsoft gets to put their fingers into it and put in a meaningless EULA. Bleh.
EDIT: You can also get the XNA 3.1 redistributable
hereEDIT: Updated to match the newest download link.
EDIT: Smaller files available:
Part 1Part 2Part 3Part 4