Theres a kernel module for it, called ndb, provided by QEMU. Thus, for it to work, you'll need to modprobe-it. Do as follows:
# rmmod ndb # just to be sure # sudo modprobe nbd max_part=16 # particularly important
Then, run qemu-nbd to map it:
# qemu-nbd -c /dev/nbd0 /media/Arquivos/XP_System.vdi
Now, the partitions will be available under /dev/nbd0pX (where X is the partition).
For e.g.:
# mount -t ntfs -o users,umask=000 /dev/nbd0p1 /media/Arquivos/XP_System.vdi /mnt
You can also use, I don't know, fdisk, maybe:
# fdisk -l /dev/ndb0
It'll list the available partitions.