Press the "F7" key to open the menu and toggle the mod. You can edit the menu key and other options in the ini file that is created in your root folder when the mod is launched.
Changes in v0.25a - Configuration file added that will generate in your root folder and in which you can set the menu key, zombie spawning number, etc.
NOTE If the zombies spawn somewhere else not near you, make sure you toggle off the mod, press Insert to reload the script and toggle the mod on again, it should fix this.