I’ve done tons of work with Rails on IIS. The bottom line is that it’s not worth it right now, as FastCGI is not a good, scalable way of deploying Rails. It works ok for a single application, but things start to get messy with multiple apps
The best aproach is to deploy Mongrel on the Windows machine and then use Apache + mod_proxy_balancer. I’ve posted lots of stuff on this before. Various setups for Windows-based deployments are also outlined in the next beta release of Deploying Rails Applications. ( http://www.pragprog.com/titles/fr_deploy). In that book, I explain how to graft Rails apps onto an existing IIS server so you can share certificates or even move the apps to a Linux box or other machines so you can actually scale upwards.
If you want to talk specifics, don’t hesitated to contact me off-list. I’d be glad to share information with you.