Cygwin is a Unix like environment for Windows. Of course this cannot completely emulate Unix, because it is not Unix. The docs for IO:Tty clearly state that this module does not work under Windows, but that it can work now under Cygwin.

Update: I like the Anon Monk question. Back up and tell us what you are trying to do and why you want this module. There may be another way to do what you want. I've used Cygwin before and this adds a significant layer of complication. I wouldn't do that unless you really have to do it.