for starters i'm prety sure you will have to export your XDCam to ProRes.
XDCam is gop-based and probably impossible to do a frame rate conversion on.
but i'm no expert!
you can use then use compressor to convert,
it's free, but very slow, i beleive.
OR you can use the Graeem Nattress Standards Converter plugin for FCP.
highly reccomended by those who have used it.
nick