Hi Nelson,
I've just worked out how to do this myself.
I did it as a sub-site to my main site (http://www.intuitiveit.com.au/subsite) but I'm sure it will work for top level sites too.
Due to the way that DNN handles host headers (so you can have multiple portals under one instance) and the way solpart menu generates its URLs, there are some gotchas that need to be addressed.
1. On the apache box, in the httpd.conf the proxypass and proxypassreverse must point to the same value as the servername. This is to ensure the solpart menu reflects the correct url. See the example here
<VirtualHost>
ServerName www.intuitiveit.com.au
ProxyPass / http://www.intuitiveit.com.au/
ProxyPassReverse / http://www.intuitiveit.com.au/
</VirtualHost>
2. On the apache box, enter a line in the hosts file to point to the backend IIS server:
192.168.0.1 www.intuitiveit.com.au
3. On the IIS server, make sure the directoryname that contains the DNN code IS NOT the same as the URL you are using.
The right way:
Directory name c:\inetpub\wwwroot\intutiveit\dnn
Portal alias subsite
The wrong way:
Directory name c:\inetpub\wwwroot\intuitiveit\subsite
Portal alias subsite. You will get an infinite redirect loop if they are the same
4. Create a virtual directory under the Site Root called subsite and point it to c:\inetpub\wwwroot\intutiveit\dnn
5. Create your new portal in DNN Host settings and make it www.intuitiveit.com.au/subsite
That's it. Good luck