Another away to install it would be
1. Install IIS7 or IIS 7 Express, and .NET 4.
2. Download Orchard.Web release from the downloads sections here on codeplex
3. unpack the archive and have a web app point to where you extracted orchard.web.
4. make sure your webapp's app pool is configured for asp.net 4.
5. browse to your web app url.
You are installing on your machine using Web Platform Installer.
Orchard does not run on linux AFAIK.
I don't know of any SaaS provider for Orchard, but I'm sure others in the community might be able to help you out.