From Steve Castledine:
You can import the HTML as a MIME entity like so:
'Put your text/html content from browser editor output into temporary field - for this example field "contenttmp"
'Get handle to tmp field
Dim tmpitem As notesrichtextitem
Set tmpitem=doc.GetFirstItem("contenttmp")
'Remove original rich text output if it is called "content"
Call doc.RemoveItem("content" )
'Stream in your text/html - richtext field will accept it properly and when you view in notes it will be formatted
Set mime = doc.CreateMIMEEntity("content")
UTF-8", ENC_NONE)