Word 2003 SP1
If I have Selection.Start = x and Selection.End = y, the
Selection.Text doesn't properly operate on data if that Range includes
fieldcodes.

Please try the following:
In a new document put the letters "abcd"
Now after 'b', insert a Date fieldcode.
Now add and run this macro:

Private Declare Sub Sleep Lib "kernel32" _
    (ByVal dwMilliseconds As Long)
Private Sub try()
   Dim doc As Word.Document
   Dim pos As Integer
   Set doc = Application.ActiveDocument
   Debug.Print Len(doc.Range.Text)
   For pos = 0 To Len(doc.Range.Text)
       doc.Range(pos, pos + 1).Select
       Selection.Font.Color = wdColorRed
       Sleep 500
   Next pos
End Sub

Notice:
1) 'a' goes red on 0, 'b' on 1, the entire date goes red on '2'.
2) 'c' is never reached, even if the For loop is set to Len+2 or
doc.Characters.Count, etc.

Try toggling the field code to get this text:
    ab{ DATE   \* MERGEFORMAT }cd
Then re-run (change color to Blue to see the diff between runs).
Note that the selection goes through each character of the field code
but stops at the "}".  By adding more characters to the end of the
string ('cdexxxxxxxxxxxxxxxxxz') and setting the Range end from pos+1
to pos+20, somehow the routine above eventually runs through the whole
string.

My application: I have a Selection of text and I know that at the end
of the selection there should be some specific character, but when I
look at the end of the selection I may or may not see these characters
if the selection happens to include a field.  I don't want to code a
cludge around this - any ideas?

Thanks.
Tony