Windows 7: moving outlook express email to IMAP folders

Hello my father has been using outlook express for years downloading his email via POP3 from seznam.cz server. Now he got a notebook so he has a desktop and notebook and he wants to have his sent emails on both machines because he frequently checks what he sent to who. So I thought I will switch settings to IMAP and it will be synchronized with server and both machines. It seems to be working, but I cannot figure out how to move local folders into the IMAP account. I tried in the old Outlook Express and also in Windows Live mail on the notebook ith Windows 7 and it cannot be done just by mouse. He has a lot of folders in a tree structure so it would be great if I could somehow populate IMAP folders with these. Any ideas? Thanks

actually I want to have just Sent email folder to be IMAP synchronized. The old received can remain as a local folder. There is a big folder tree in a sent email folder though...

I think it may depend on the email provider's web interface. In other words go to the email website interface of your provider to see if they have a sent folder and also allow you to add subfolders under it. They may also require you to set something that says "save a copy of sent items in sent file folder" on their website. In other words it may be that you can't force folders on to the server from the local mail program but the local mail program can be set up to display what is already on the server.