cannot copy to external hdd

Can you give the ouput of:

sudo fdisk -l; mount

What XP does or doesn't do is of no interest to us.

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000001

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 2893 23237991 7 HPFS/NTFS
/dev/sda2 2894 19457 133050330 5 Extended
/dev/sda5 2894 18779 127604263+ 83 Linux
/dev/sda6 18780 19457 5446003+ 82 Linux swap / Solaris

Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x44fdfe06

   Device Boot Start End Blocks Id System
/dev/sdb1 1 60801 488384001 c W95 FAT32 (LBA)
/dev/sda5 on / type ext4 (rw,errors=remount-ro)
proc on /proc type proc (rw)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
udev on /dev type tmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
none on /var/lib/ureadahead/debugfs type debugfs (rw)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev)
/home/esben/.Private on /home/esben type ecryptfs (ecryptfs_sig=5f2a9a8e22930e28,ecryptfs_fnek_sig=c804a8c27650edc6,ecryptfs_cipher=aes,ecryptfs_key_bytes=16)
gvfs-fuse-daemon on /home/esben/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=esben)
/dev/sdb1 on /media/My Book type vfat (rw,nosuid,nodev,uhelper=devkit,uid=1000,gid=1000,shortname=mixed,dmask=0077,utf8=1,flush)
esben@esben-laptop:~$

Ok here is the bit we need:

/dev/sdb1 on /media/My Book type vfat (rw,nosuid,nodev,uhelper=devkit,uid=1000,gid=1000,shortname=mixed,dmask=0077,utf8=1,flush)

the uid is 1000 which is the first user you created when you setup the computer. Are you using that user?

Aha! I think I understand. No, this is not the same. What can I do?

Ok you can either edit /etc/fstab to add an entry for the partition to mount as owned by the UID of the new user or you can do some jiggery pokery in gconf which I am not conversant with but I am sure guides do exist.