CSV is the correct format to use, but al long as you mapped you mapped your
fields correctly when you exported, then your problem is in OE. You'll need
to ask in an OE group. This is a group to support Outlook from the Office
group of programs. Outlook Express is a part of Internet Explorer and is a
quite different program despite its similar name..

You will probably get a faster and more expert answer if you post this to an
outlook express news group.

Try posting in one of these newsgroups:
microsoft.public.windows.inetexplorer.ie5.outlookexpress for OE 5.x
microsoft.public.windows.inetexplorer.ie55.outlookexpress for OE 5.5x
microsoft.public.windows.inetexplorer.ie6_outlookexpress for OE 6.x

A good website for information on OE is:
http://www.tomsterdam.com/