UrlRewriting for Subdomains

In IIS7 using UrlRewrite module I want to do something likes this. I tried everywhere, possibly this is wellknown problem, but couldn't find any usefull solution.

Url "http://tom.mydomain.com" should be read internally as "http://mydomain.com/dashboard?g=tom"开发者_JS百科

I am using ASP.NET MVC, just in case info is required.

---

Finally, we have configured our own DNS server to handle this issue. So this question is no longer in my case. However, this seems to be not a good idea to rewrite such url. The Application Request Routing feature in IIS7 is one way to go