Hi Pawel,
We do this daily with the Sony XDCam Transfer for FCP plug-in. You can download it from Sony's Pro site (direct link:
http://bit.ly/PekAHy). It's listed as "PDZK-P1 XDCAM Transfer Software". Once this is installed, a new option will appear in FCP's Export menu entry, named "Sony XDCam", rather appropriately. This will bring up a dialog where you can select the container (MXF in your case) and the settings.
I've only ever done this with HD material and you don't specify anything about format, so your mileage may vary.
IHTH,
JC Boulay
Technical Director
Audio Z
Montreal, Canada
http://www.audioz.com