Creating a top level web site in Windows SharePoint Services

Hi, everybody. It is the first time I use Windows SharePoint Services and I am facing the following problem:

Iam logged in as Administrator (this is user name), I am trying to create a web site and in the field user name I put Administrator an error message appears “The user does not exist”. The PC I am working on does not belong to a domain but to a workgroup named ICSYSTEMS. I followed the example and put ICSYSTEMS\Administrator but the message is now “The user or group ICSYSTEMS\Administrator is unknown”.

The operating system is Windows Server 2003 enterprise edition.

Is it necessary that the PC belongs to a domain?

Thanks in advance