Is it possible to install Indigo on a Windows 7/8 machine and do prototyping for an iPad application, or does Indigo have to be installed on a Mac to do Mac-like prototyping, and Windows to do Windows-like prototyping?
Thank you for your question. Short answer is yes.
Long answer is that Indigo runs on both Windows and Mac exactly the same. It's the exact same app. You can start your work on a Windows version and continue on a mac or in reverse. The prototypes created will work just the same on any platform as these are rendered as HTML. So all you need is a web-browser to run it outside of the Indigo Studio application.
Once you are done with building your prototype, you can either use the SHARE option to securely publish it on Infragistics server. The server provides you with a link that you can send to anyone. The other option is to publish it as an offline prototype.
Learn more about sharing/using your prototype here: :http://indigo.infragistics.com/help/sharing-your-prototypes.html
Let us know if you need more clarification.