MySql Field Update

Why is it that this does not work in MySql?

RS.Fields("Fullname").value = "Bob"

Is it because MySql does not support this?

The code below is a bit more representative of what I'm doing:

<!--#INCLUDE FILE="Database_Open.asp"-->
<%
sql ="SELECT * FROM CustomerBase WHERE " & _
"UserName='" & username & "' AND " & _
"SECRETWORD='" & password & "' "

RS.Open Sql, Connection, 3

IF RS.EOF THEN
'redirect code here
ELSE
RS.Fields("Fullname").value = "Bob"
RS.Update
%><!--#INCLUDE FILE="Database_Close.asp"--><%
Response.Redirect ("Menu_Account.asp")
END IF
%>