I have IMAP account. All the messages I have in user.pavel are shown in KMail as Inbox. I have special folder named user.pavel.Sent to store sent messages.

IMAP account
- Inbox
- - Sent

I have set the folder user.pave.Sent as the folder to store sent messages and it have been marked the same icon as Sent in my local folders. But it stay inside my Inbox.

I think it is not very nice to have folder Inbox/Sent (it is not semantically right). So, have I a way to show Sent folder not inside Inbox, but at the same level:

IMAP account
- Inbox
- Sent

Unfortunately due to the way the IMAP server you are using works, there is no way around the issue. KMail simply displays the folder structure as given to it by the IMAP server, and will probably refuse to implement any hacks which allow the user to make local changes to the folder structure which are not shown on the server.

I would recommend contacting the IMAP server administrators for assistance in this matter.
Alternately, if you are the Administrator, please consult the documentation for your IMAP server, or ask on one of their development lists.