Many hosting companies won't install ISAPI filters for you on a shared hosting account. isapi_rewrite is a must-have requirement for Wordpress on IIS with proper SEO in mind. (IMO it's a requirement for proper SEO on any IIS server.)
So if your hosting soltuion doesn't/can't/won't support isapi_rewrite then WordPress on IIS is a bad choice if you're hoping for decent search engine listings. You're better off finding a company that's familiar with WordPress on Linux/Apache. It will most likely be cheaper too.