SubDomain in IIS

I assume that
A. you have a single IP Address to work with (say 1.2.3.4)
B. the default web site is www.yourdomain.com and is pointing to c:\websites\your.com\
C. DNS server setup.
1. Open IIS manager, and check the properties of the default web site.
2. in 'web site' pane, click 'advanced' button next to ipaddress.
3.Select the first item in the top box, click edit
4. set ipaddress = (for example) 1.2.3.4, port 80, and www.yourdomain.com as host header.
5. ok and close all property panes.
6. right click iis->computer->new->web site
7. click next, enter some description, next.
8. select ip address (eg) 1.2.3.4 (same as the default) port 80, host header name ="sub.mydomain.com". Use the default port 80. else you have to use www.yourdomain.com:portNO/
9. enter path (eg) C:\websites\yourdomain.com\sub\
10. finish and close property panes.
11. in your DNS server, add the hostname "sub.yourdomain.com" with ip the relevent address (eg) 1.2.3.4 (same as the default)once the dns propogates (depending on where you are, it may take up to a day or two) then you will find that http://sub.yourdomain.com will open your sub web site.