Hi Andria,
DotNetPanel doesn't really require you to use a "domain" type for all domains but your host probably set up DotNetPanel (DNP) to only give you the "domain" option. Depending on the version of DNP, you should be able to specify your subdomains as "Web Site Pointers." "Web Site Pointers" are added by clicking the Websites link in the menu on the left of your control panel and then selecting the Website from the list. You should see a button that reads "Add Web Site Pointer."
If you can't use a sub-domain or full domain as a "Web Site Pointer," you need to get your host to allow you to create "Domain Aliases" or "Domain Pointers" (DNP used pointers for a while and then switched to aliases). Once you have a "Domain Alias" you can use that as a "Web Site Pointer."
To match things up to the documentation here on mojoPortal, a "Web Site Pointer" in DNP-speak is really a host-header or a binding. It really would be nice if everyone used the same terminology but then the Marketing guys would be out of jobs.
As a side-note, DotNetPanel was release as OpenSource back in April '10 and renamed to WebSitePanel. You can find documentation on it here: http://www.dotnetpanel.com/documentation/ and here: http://websitepanel.net.
I implemented DotNetPanel/WebsitePanel at my hosting and mojoPortal design company, i7MEDIA (http://i7media.net), a few years and my customers really like it. I am working on some nice videos for customers to use for help with the control panel but, we really push customer service and try not to just point people to knowledgebase videos or articles.
HTH,
Joe D.