This is not an exact answer because I am not sure of your server variables but here is something that might be useful to you. Here. This walks through the IIS set up for version 7 and it has some basic concepts. There is rewrite module/tool that could help but I haven't used it. And another document here...Shows the GUI interface like the first link and is in 7.5.
Again not specific solutions but hopeful you have some server gurus there that can help you at least get the IIS settings right (or at least not sound dumb if you have to communicate something specific to them) if this is a first time IIS Isapi venture for you.