Unable to add folders to send/receive group?

I've just upgrade from Outlook 97 to Outlook 2003.

Everything seemed to work fine, my folders and contents were copied across
with my Internet Mail accounts.

However when I try and send a new mail message it stays in the 'Outbox' and
isn't sent.

I've checked my Send/Receive Group settings and the only thing that seems
odd is that my Send/Receive Folder Options is only showing the 'Inbox' folder.

I've tried to add my other 10 folders to this list, but I am unable to (I
would expect the 'Outbox' folder would need to be configured in here, but it
isn't and it won't let me).

Am I barking up the wrong tree?

Can anyone help?

Regards

Paul