Cisco IOS-On-UNIX is a fully working version of Cisco IOS that runs as a user mode Linux process.
IOU supports all Cisco IOS platform independent protocols and features. IOU allows you to build out a network topology on a single PC without the need for physical routers. This is useful for validating network designs, proof-of-concept testing, and certification self-study.
This is the Linux-based version, this application run only in Linux. If you are a MS ShiChuang user, you can install a Linux operating system in a dual boot scheme or in a virtual machine such VirtualBox or Vmware Workstation.
Here are some tutorials. Please, pay special attention to the chapter of Cisco IOU Error Messages.