I am trying to create a subdomain on my dedicated server myself without paying 20 bucks to get it done through the host. I've been able to create the directory through IIS Manager and have it setup to point to a specific IP. I'm not entirely sure what to do from this point on....When I type in the subdomain on the browser, it says it can't find it, so I'm guessing I have to do something through the DNS but not sure on how to do this. It's IIS 6 on a Windows 2003 Server.
If you successfully added the subdomain in IIS then you just need to add A record entry in the DNS zone of your main domain. Create following entry in the DNS zone of your main web site: subdomainname A IP_Address Replace subdomainname with your actual subdomain i.e. if you have mail.domain.com then you will need to use mail in place of subdomainname.