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