Talib wrote:

But how can one change the pst file format. You know when we install
outlook 2003
pst file format remains the same i.e personal folder file 97-2002
which supprots only 2gb of data. Now if I want to work on higher
version of pst file which can grow as big as upto 20gb, I'll need to
create a new pst file. So one way to access old mail data is either
to let them remain in the old pst file or to import them in the new
one. What do I do?

Described here many times. Google Groups is your friend.
http://groups.google.com/group/microsoft.public.outlook.general/msg/fe4f6aecf94baeff
--
Brian Tillman