URL rewrite SubDomain to folder

Hi,
I am using URL rerwriter to link my subdomain to a folder under the path
folder1/folder2/subdomainfolder. I have the code:

Code:

<rule name="devmy.xx.com">
                    <match url=".*" />
                    <conditions>
                        <add input="{HTTP_HOST}" pattern="^(devmy.)xx.com" />
                        <add input="{PATH_INFO}" pattern="^/devmy/" negate="true" />
                    </conditions>
                    <action type="Rewrite" url="\folder1\folder2\subdomainfolder\{R:0}" />
                </rule>

Which works fine for the first page and then if that page calls a page2 I get the url:
http:\\devmy.xx.com\folder1\folder2\subdomainfolder\page2.aspx which of course does not exist.
How do I stop it adding the folder structure for all pages i.e. how do I make the subdomain appear as a base domain for this site?