You can programmatically add a Content Editor Web Part (CEWP) to a a SharePoint 2003 WSS page.
Let's assume that you've already opened a WSS site by using the openWeb() method. Add the following code:
ContentEditorWebPart MyCEWP = new ContentEditorWebPart();
MyCEWP.ZoneID = "Left"
MyCEWP.Title="Web part title"
MyCEWP.FrameType= FrameType.TitleBarOnly;
MyCEWP.PartOrder = 2;
XmlDocument xmlDocxmlDocMyCEWP = new XmlDocument();
XmlElement xmlElementDetails = xmlDocxmlDocMyCEWP.CreateElement("NewCEWP");
xmlElementDetails.InnerText = "<p><b>My new web part</b><br />Lots of text here…</p>"
MyCEWP.Content = xmlElementDetails;
Having created the above web part you must also add it to the page:
SPWebPartCollection webPartCollection = TheWSSweb.GetWebPartCollection("default.aspx", Storage.Shared);
webPartCollection.Add(MyCEWP);
ThisWSSweb.Update();
You need to reference Microsoft.SharePoint.WebPartPages and System.Xml in order to make the above example work.