I believe the problem is with the XF file system. If you are using NTFS, you cannot write via Linux yet. (I believe that this is being worked on.) If however, you have a VFAT file system, you should be able to write successfully.
That's the situation on my dual boot system. I can write just fine to my VFAT partition, but not to my NTFS partition.
Joel
Want to buy your Pack or Services from MandrakeSoft? Go to http://www.mandrakestore.com