Hey Tom.
Your issue is that you have SharePoint 2003 and that tutorial is for 2007.
I would look at the AD Web Service here http://www.qdabra.com/en/products/ADWebService.aspx
You can checkout the video or the documentation. It gives you not only name, but email, address, manager, what ever is in Active Directory. This can be a big benefit in most forms to be able to complete forms for people and be able to identify the form user for auditing and security.
There is a funky way to get the person's name but that is all you can get from SP2003.
It involves submitting to SharePoint on Open.
Query Library for filename that you submitted the form as
Delete the file form the library using a CAML.
Then filter the created name from the SharePoint list data.