my 2 cents....

No offense to your partner or anyone else with the same opinion, but...
Installing and CONFIGURING Sharepoint and then DotnetNuke will produce the answer to your questions.
A intermediately skilled user/developer can install DNN and have the default page running in 15 minutes, less actually.
Sharepoint really requires a lot more system administration/networking skills.

Sharepoint and DotNetNuke provide 2 very different platforms and features.
They should be used together instead of trying to pick only one.
If there will not be heavy use of the Office 2003 integration there is no reason to use Sharepoint.

Sharepoint
Best use is in an Intranet environment with Active Directory.
Excellent interaction with Microsoft Office 2003, especially Excel & OutLook.
Excellent Active Directory integration.
WSS is free with Windows Server 2003.  This is more than adequate for small sites.
More difficult to write custom modules (webparts).
Painfully difficult to create a clean looking website.

DotNetNuke
No licenses required. (MS SQL only)
Full source code.  Not many valid reasons to modify the core but the code is an excellent source of "how to" do everything.
Excellent application development platform.  Sharepoint does not come even close.
Modules (user controls) can be written in vb.net or c#.
Skinning engine provides unlimited control over the look of your site.
Hundreds of inexpensive modules that save 100's of development hours.

How to use both
Since Sharepoint steps all over the "default" website it is difficult to get DNN working as an excluded virtual folder. 

Create a new website with its own IPAddress, url and application pool.
DNN will work just fine and both platforms are completely separate.

mikez