I have DNN 4.7 installed on Windows XP and SQL 2005. Recently I had the need to test parent and child portals to simulate changes that will be done on a site. The following is a list of steps I took to configure muliple parent portalss in XP.
Step 1: XP is website challenged.
XP out of the box allows only one website to be configured. The functionality to add new websites is not exposed via the MMC interface. To be able to create multiple websites in XP follow the instructions on this page.
http://weblogs.asp.net/stevencohn/articles/59782.aspx
Step 2: Install DNN in the newly created website
After following the instruction for step 1, install DNN in the newly created website or point to an existing installation. Make sure to change the ASPNET framework to 2.0 since it defaults to 1.1.
step3: Host File modifications
Fake a few entries in your C:\WINDOWS\system32\drivers\etc\hosts file for your Parent portals all pointing to
127.0.0.1 www.parentportalone.com
127.0.0.1 www.parentportaltwo.com
Step4: Go to DNN and create the parent portal www.parentportalone.com.
Create as many portals as necessary - the only requirement is to have them defined in your host file. After doing this you'll be able to browse www.partentportaone.com or whatever entry you have created and DNN will do its magic.
I have sucessfully tested this with 6 parent portals.
Hope this helps.