When I try to install on Windows 2003 I get the error that states:

Using Windows Explorer, browse to the root folder of the website ( C:\DotNetNuke by default ). Right-click the folder and select Sharing and Security from the popup menu ( please note that if you are using Windows XP you may need to Disable Simple File Sharing before these options are displayed ). Select the Security tab. Add the appropriate User Account and set the Permissions.

• If using Windows 2000 - IIS5
  
  1. the [SERVER]\ASPNET User Account must have Read, Write, and Change Control of the virtual root of your website.
• If using Windows 2003 - IIS6
  
  1. the NT AUTHORITY\NETWORK SERVICE User Account must have Read, Write, and Change Control of the virtual root of your website.

The problem is that in the file system - right click the root and go to add the NT AUTHORITY\NETWORK SERVICE user it reports back that the user does not exist for the domain:

The following object is not from a domain listed in the Select Location dialog box, and is therefore not valid:
 NT AUTHORITY\NETWORK SERVICE

any ideas? can I change the user under which the install takes place?

Or simply type it in, you don't need to select it from a dropdown.

Jeff